user131: In a large number of religions, 'good' and 'bad' are defined by some all-powerful diety who either sends a representative or himself to tell us about what exactly they want us mortals to do.
In Buddhism, instead an enlightened individual basically worked it all out.
So the basic question is - why does that happen? What decided that killing (even if your intentions are good*1) will cause something negative ? What about the other actions? There is no 'final judge' to confirm or deny we've followed a particular path - so why does the universe (?) act this way? And what makes us sure that we're correct?
*1 - It's an impression I got from reading some other answers, if I'm wrong on this please do correct me)

user9861: In Buddhist psychology, there is a very realistic answer to this question in terms of kusala sankhara and akusala sankhara. In essence, kusala sankhara consists of those causes of actions that are based upon awareness, knowledge, and compassion, while akusala sankhara consists of those causes of action that is somewhat lacking one or more of these qualities. The reality is that the causes of either form of behaviour are very complex, intelligent, and mostly unconscious.



Why does that happen?

Understanding the causes of human behaviour and human intelligence is a vast study. The Theravadin Abhidharma and modern psychology are examples of such studies. You ask the question as if there is a simple answer. Causality is complex and there is no simple way to characterize it.



What decided that killing (even if your intentions are good) will cause something negative?

Wrong question. The only knowledgeable question to ask is: How does an intelligent and well-informed person decide the psychological consequences of a particular instance of killing? The answer: He decides on the basis of a whole lot of background information. How can you expect otherwise? In psychology, there is no “what” that decides anything.



What about the other actions?

Same answer as #2, above.



There is no 'final judge' to confirm or deny we've followed a particular path - so why does the universe (?) act this way?

In psychology, there is no final judgement, only a very carefully qualified estimate. The universe does not perform actions. Only persons (and perhaps some animals) perform actions.



And what makes us sure that we're correct?

When it comes to psychological explanation, certainty is never an option. It sounds like you are talking about the attitude of a dogmatic guru. If so, I suggest you find another guru that does not have a deep psychological need to feel superior to you.



user290: Suffering/samsara is "bad". The end of suffering/nirvana is "good".
Therefore, whatever is conducive to enlightenment is "good", while whatever leads one away from it is "bad".

user143: Part of what makes an action good or bad is the intention.
Actions taken with unwholesome intentions such as these from "The Roots of Good and Evil" can be considered bad actions:

Greed — liking, wishing, longing, fondness, affection,
  attachment, lust, cupidity, craving, passion,
  self-indulgence, possessiveness, avarice; desire
  for the five sense objects; desire for wealth,
  offspring, fame, etc.
Hatred — dislike, disgust, revulsion, resentment, grudge,
  ill-humour, vexation, irritability, antagonism,
  aversion, anger, wrath, vengefulness.
Delusion — stupidity, dullness, confusion, ignorance of
  essentials (e.g. of the Four Noble Truths),
  prejudice, ideological dogmatism, fanaticism,
  wrong views, conceit.

Actions taken with wholesome intentions such as these, from the same book, can be considered good actions:

Non-greed — unselfishness, liberality, generosity; thoughts
  and actions of sacrifice and sharing; renunciation,
  dispassion.
Non-hatred — loving-kindness, compassion, sympathy,
  friendliness, forgiveness, forbearance.
Non-delusion — wisdom, insight, knowledge, understanding,
  intelligence, sagacity, discrimination,
  impartiality, equanimity

However there is also a factor of the end result. Some actions taken with good intentions can lead to suffering while some actions taken with bad intentions can turn out actually well for someone. So in another sense, actions which lead to suffering are bad actions and actions which lead to freedom from suffering are good actions.

user4740: In my understanding, which is imperfect, in a Buddhist understanding of reality, there is no absolute moral ground to find or be found on, no inherent "way of life" to live up to or learn, no true measure of worth or worthiness, no true absolute bar or standard of what is to be considered inherently good or bad, no central value judgement system, and therefore nobody to communicate that system to us from some sort of divine moral source. 
It is up to each individual to discover first hand what is beneficial, what is wholesome, what is skillful, what is good. We decide what that measure should be, and set it simply based off of experienced reality: good is what liberates us and alleviates the experience of suffering, bad is what confines and deludes us, that which increases the experience of suffering. Good and bad, therefore, can be inferentially equated to ignorance vs. awareness of what our true nature is really all about. This can be brought back to an awareness of the lack of inherent good or bad value.
So, good is that which is in line with this awareness of a lack of inherent goodness, and bad can be thought of in terms of ignorance, or the deluded notion that things have an absolute positive or negative value. This is tied into relativism, into emptiness via dependent origination, to interdependency, to what Thich Nhat Hahn calls interbeing. We have a good and bad, but it is merely a convention, in no way absolute. We can say that, as long as we have apparent existences, causing pain and suffering to others merely furthers our own misery, and misery in general, and ought to therefore be considered a "bad" or non-beneficial action.
If you know, and by "know" I mean like how you know that breathing is good and sleep is nice, what your true nature is, then you will understand on an intuitive level how to free yourself from and avoid ultimate suffering, and what is the absolute extinguishment of all suffering? :) This is the same as if you know that a fire burns from first hand experience, you call the act of sticking your hand in a fire bad, due to the effect that that will have: suffering.
This happens, clearly, because certain causes have certain effects. For instance, if you commit a horrible act to someone, you will eventually come to grips with the notion that this was a human, like you, vulnerable and suffering the vicissitudes of life. This will bring about the experience of suffering, and will cause you to either become numb or more sensitive. It must be contended with in some way. This is a form of suffering.
More so, you were suffering before you committed the act that led to further suffering. In other words, you had a feeling of suffering that acted as the motivation behind an act. That intention/motivation/feeling of suffering becomes stronger when you act on it, though we are seeking to satisfy ourselves. So it is understood that, ultimately, it is this intention that defines an act as having moral value, it is intention that creates good or bad karma, also perception, also effect. However, in Buddhism, the "aim" is to free yourself of karmic conditioned existence. It is seen that even "good" karmas are the causes of suffering, and are just a part of the truly good or truly bad trap.
So, are your actions set with the intention of extinguishing suffering? If so, with a correct understanding of what causes suffering, then they might be beyond karmic consequence. Are they set with the notion of true existence and value? If so, they will likely act as seeds, as cause for immediate or future suffering, and are ultimately non-beneficial towards the goal of ultimate, final liberation.
Question must be in the "why" of things, and have room for weather or not the apparent actor is aware of the consequences or effects of the actions that are being committed in the name of said intention. So, is there a killing where the intention was truly beyond the perception of absolute good or bad, motivated purely by compassion and free from all misapprehension and motivational suffering? I can't answer that for you, but I cannot imagine myself in a situation where a killing would not lead to more suffering. What decided that? I would argue just the bare, basic, un-elaborated, simple ole truth of our lives.
Remember, positive and negative are subject qualifications and are based on pleasure and pain, which are also subjective. We cannot value things in any absolute way given those truths. The universe does not judge you, you do a fine enough job doing that yourself.
There's a great story, and I will have to find the sutra this comes from, where a man came to the Buddha asking him to help, there was a dire situation. This man's brother (or some relative) had died, and they had not performed the necessary rights to ensure a safe passage to a heavenly afterlife, or good rebirth. He knew of the Buddha's fame as a sage and teacher, so thus sought out his expertise, certain that the great Buddha could alleviate this misfortune. 
The Buddha instructed the man to go get two very light weight "jars", and fill one with melted churned butter, and the other with rocks, and bring them, with the body, to the river. Excited, the man did this, believing the Buddha would surely help his brother. 
When he came back, the Buddha was waiting for him, and instructed him to place both jars in the river, and when he did so, they just floated there, slowly drifting away. The Buddha then broke open the first jar, and the butter stayed on top of the river as the jar broke. It frothed up, and was carried away. Then he broke the other jar, with the rocks, and the rocks all sank down after the jar was broken.
He told his new friend that there is nothing that anyone can do after the life is over. Only the weight of our good or bad deeds determine where we go in rebirth, as it does so from moment to moment in this life. 
Our actions leave impressions in our consciousness, in our minds and on our hearts, based on our own sense of value judgements, which are based on our own sense of what is truly real and existent. These impressions carry us away, or sink us down. How is it not the case? 
The trick is transcendence, to develop an awareness of the true nature of reality (anatta, anicca, dukkha) and get your intention fixed in a alignment with it. This is done by following the 8 fold path, and the morality section is based off of simply making it so that there are no mental distractions that will keep you from developing your awareness. As such, they are based off of non-attached, dispassionate, compassionate social activity. They are aimed at selflessness.
Karma is based off of volitional reactive activity to perception driven feelings, the quality of those feelings, and our relationship to them in terms of either our tolerance to them, or their influence over us. To reduce blind volitional reactivity, we can develop awareness and equanimity via meditation.

user43: "why does that happen? What decides that killing (even if your intentions are good) will cause something negative ? What about the other actions? why does the universe act this way?"
As some answers correctly say, an action is bad when it leads to suffering, imprisonment, and confusion - and good when it leads to peace, freedom, and correct understanding. But why? What makes an action wholesome or unwholesome?
The nature of suffering, imprisonment, confusion - is conflict. A mismatch between how things are and how you want them to be. A conflict between you and the world. A conflict between people. An inner conflict in one's psyche. 
The nature of peace, freedom, truth - is no conflict, no mismatch between expectations and reality, between us and them, no inner conflict, no outer conflict.
So, things that lead to conflict, to division, to mismatch - are bad. And what are these things? Lies lead to mismatch between beliefs and reality, therefore lies are bad. Divisive speech leads to conflict between people. Desire leads to unsatisfied expectations, which is a form of inner conflict. Desire also leads to conflict with people who have what you want. Hatred leads to conflict. Intoxication leads to mismatch between perception and reality. That mismatch is a form of conflict. And so on. Whatever action spreads the seeds that grow as division of people, division of mind, conflict - is going to be unwholesome. 
The same principle works for wholesome, positive action. Whatever leads to unification, to decrease of conflict, to less division, to a better match between ideas and reality, between people, and within one's own mind - that leads to harmony, to peace.
Truth, peace, love, acceptance, suchness - is conflictless. 
Non-truth, war, hatred, intolerance, dukkha - is conflict.
Conflict and conflictlessness is the key principle behind Buddhist ethics. This is what defines whether the action is good or bad, through the mechanism of cause and effect. 
Divisive action leads to division. Conflict-inducing action leads to conflict. Un-truthful action leads to conflict of information. Violence leads to conflict.
Reconciling action leads to peace. Pacifying action leads to no-conflict. 
This is the basic principle. Conflict is bad. No conflict is good.
P.S.
The nature of suffering is conflict because mind (being an informational phenomenon) does not handle logical contradictions well. So anything that leads to an experience of clash or contradiction is perceived as suffering by the mind attached to (or identifying with) one of the sides of the contradiction. Conversely, reducing the conflict leads to experience of harmony, and that's the mechanism behind 8NP. This is already down at the level of the fundamentals; I don't think there is a further why more fundamental than this.

user89: In Buddhism, the concepts of good and evil do not exist as in other religions (no being is inherently good or evil). No deity tells you what to do. There are the teachings of the Buddha, that we can make use of, as opposed to believing in a doctrine (such as "Ithe authority tells you this, therefore you should obey*"). 
However, there is still a distinction between the helpful and harmful, skillful and unskillful - in the context of the path (to liberation, nirvāṇa, nibbāna). In terms of karma (actions, kamma), there are the wholesome and unwholesome, but these are useful in terms of the actions we choose to avoid and to act on, in each given moment (now).
Mara, as mentioned in the Pali Canon, is referred to as evil (in the English translation), but even he will be enlightened one day. In other words, noone is inherently evil (or good) - no deities, ghosts, humans or other, in Buddhism. For instance, Maha Moggallana, disciple of the Buddha, mentioned to Mara at one point that in a previous existence, he had been Mara, and (the current) Mara had been his nephew. Strikingly, despite having been the "embodiment of evil in the world", a number of lifetimes later, he was one of the prominent disciples of the Buddha (Gotama).
An excerpt from the story: (source)

The first Buddha appearing in our "fortunate aeon" (bhadda-kappa) with
  five Buddhas, was Kakusanda. He lived when the lifespan of man was
  40,000 years and when the first darkening of the golden age became
  evident because of a king's lack of concern and the occurrence of the
  first theft. Because of that, man's vital energy became reduced to
  half. At that time, Moggallana was Mara, chief of demons, lord of the
  lower worlds, and his name was Mara Dusi. He had a sister by name of
  Kali whose son was to become the Mara of our age. Hence Moggallana's
  own nephew was now standing in front of him at the door post. While
  being the Mara of that distant time, Moggallana had attacked a chief
  disciple of the previous Buddha by taking possession of a boy and
  making him throw a potsherd at the holy disciple's head so that blood
  was flowing. When the Buddha Kakusandha saw this, he said: "Verily,
  Mara knew no moderation here" — because even in satanic actions there
  might be moderation. Under the glance of the Perfect One the astral
  body of Mara Dusi dissolved on the spot and reappeared in the deepest
  hell. Just a moment ago he had been the overlord of all the hellish
  worlds and now he himself was one of hell's victims. A moment ago he
  had been the greatest torturer and now he himself was undergoing one
  of those terrible torments.

Whether we believe in the details of the stories in the Pali Canon is up to each of us. However, important to note, is that we all have the ability and opportunity to choose a wiser path.
Regarding your questions (in shuffled order):

There is no final "judge". No being (God or otherwise) controls our existence.
The Buddha (through long practice) awakened to (discovered, if you will) the way things are, how this existence functions.
Upon awakening, the first inclination of the Buddha was that "noone will ever understand this" - that it's impossible to teach. However, he was persuaded that some beings could be helped, and so he decided to teach others.
Briefly explained, words are inadequate to explain the way things function (karma, and so on), so instead of preaching something to believe in, the Buddha pointed the way for each of us to find out.

So noone "decided that killing is negative" (nor did anyone decide the effects of other actions). However, Buddhists will gladly help you on the path to finding out for yourself, to discover the effects of karma (your actions). Regarding being "sure we're correct", don't just take anyone's word for it. Try it out, see for yourself, do the methods and teachings from Buddhism work for you. Only then can you find certainty.

131: <p>In a large number of religions, 'good' and 'bad' are defined by some all-powerful diety who either sends a representative or himself to tell us about what exactly they want us mortals to do.</p>

<p>In Buddhism, instead an enlightened individual basically worked it all out.</p>

<p>So the basic question is - why does that happen? What decided that killing (even if your intentions are good*1) will cause something negative ? What about the other actions? There is no 'final judge' to confirm or deny we've followed a particular path - so why does the universe (?) act this way? And what makes us sure that we're correct?</p>

<p>*1 - It's an impression I got from reading some other answers, if I'm wrong on this please do correct me)</p>
 9861: <p>In Buddhist psychology, there is a very realistic answer to this question in terms of kusala sankhara and akusala sankhara. In essence, kusala sankhara consists of those causes of actions that are based upon awareness, knowledge, and compassion, while akusala sankhara consists of those causes of action that is somewhat lacking one or more of these qualities. The reality is that the causes of either form of behaviour are very complex, intelligent, and mostly unconscious.</p>
<ol>
<li>
<blockquote>
<p>Why does that happen?</p>
</blockquote>
<p>Understanding the causes of human behaviour and human intelligence is a vast study. The Theravadin Abhidharma and modern psychology are examples of such studies. You ask the question as if there is a simple answer. Causality is complex and there is no simple way to characterize it.</p>
</li>
<li>
<blockquote>
<p>What decided that killing (even if your intentions are good) will cause something negative?</p>
</blockquote>
<p>Wrong question. The only knowledgeable question to ask is: How does an intelligent and well-informed person decide the psychological consequences of a particular instance of killing? The answer: He decides on the basis of a whole lot of background information. How can you expect otherwise? In psychology, there is no “what” that decides anything.</p>
</li>
<li>
<blockquote>
<p>What about the other actions?</p>
</blockquote>
<p>Same answer as #2, above.</p>
</li>
<li>
<blockquote>
<p>There is no 'final judge' to confirm or deny we've followed a particular path - so why does the universe (?) act this way?</p>
</blockquote>
<p>In psychology, there is no final judgement, only a very carefully qualified estimate. The universe does not perform actions. Only persons (and perhaps some animals) perform actions.</p>
</li>
<li>
<blockquote>
<p>And what makes us sure that we're correct?</p>
</blockquote>
<p>When it comes to psychological explanation, certainty is never an option. It sounds like you are talking about the attitude of a dogmatic guru. If so, I suggest you find another guru that does not have a deep psychological need to feel superior to you.</p>
</li>
</ol>
 290: <p>Suffering/samsara is "bad". The end of suffering/nirvana is "good".
Therefore, whatever is conducive to enlightenment is "good", while whatever leads one away from it is "bad".</p>
 143: <p>Part of what makes an action good or bad is the intention.</p>

<p>Actions taken with unwholesome intentions such as these from <a href="http://www.buddhanet.net/pdf_file/roots_goodevil.pdf" rel="nofollow">"The Roots of Good and Evil"</a> can be considered bad actions:</p>

<blockquote>
  <p>Greed — liking, wishing, longing, fondness, affection,
  attachment, lust, cupidity, craving, passion,
  self-indulgence, possessiveness, avarice; desire
  for the five sense objects; desire for wealth,
  offspring, fame, etc.</p>
  
  <p>Hatred — dislike, disgust, revulsion, resentment, grudge,
  ill-humour, vexation, irritability, antagonism,
  aversion, anger, wrath, vengefulness.</p>
  
  <p>Delusion — stupidity, dullness, confusion, ignorance of
  essentials (e.g. of the Four Noble Truths),
  prejudice, ideological dogmatism, fanaticism,
  wrong views, conceit.</p>
</blockquote>

<p>Actions taken with wholesome intentions such as these, from the same book, can be considered good actions:</p>

<blockquote>
  <p>Non-greed — unselfishness, liberality, generosity; thoughts
  and actions of sacrifice and sharing; renunciation,
  dispassion.</p>
  
  <p>Non-hatred — loving-kindness, compassion, sympathy,
  friendliness, forgiveness, forbearance.</p>
  
  <p>Non-delusion — wisdom, insight, knowledge, understanding,
  intelligence, sagacity, discrimination,
  impartiality, equanimity</p>
</blockquote>

<p>However there is also a factor of the end result. Some actions taken with good intentions can lead to suffering while some actions taken with bad intentions can turn out actually well for someone. So in another sense, actions which lead to suffering are bad actions and actions which lead to freedom from suffering are good actions.</p>
 4740: <p>In my understanding, which is imperfect, in a Buddhist understanding of reality, there is no absolute moral ground to find or be found on, no inherent "way of life" to live up to or learn, no true measure of worth or worthiness, no true absolute bar or standard of what is to be considered inherently good or bad, no central value judgement system, and therefore nobody to communicate that system to us from some sort of divine moral source. </p>

<p>It is up to each individual to discover first hand what is beneficial, what is wholesome, what is skillful, what is good. We decide what that measure should be, and set it simply based off of experienced reality: good is what liberates us and alleviates the experience of suffering, bad is what confines and deludes us, that which increases the experience of suffering. Good and bad, therefore, can be inferentially equated to ignorance vs. awareness of what our true nature is really all about. This can be brought back to an awareness of the lack of inherent good or bad value.</p>

<p>So, good is that which is in line with this awareness of a lack of inherent goodness, and bad can be thought of in terms of ignorance, or the deluded notion that things have an absolute positive or negative value. This is tied into relativism, into emptiness via dependent origination, to interdependency, to what Thich Nhat Hahn calls interbeing. We have a good and bad, but it is merely a convention, in no way absolute. We can say that, as long as we have apparent existences, causing pain and suffering to others merely furthers our own misery, and misery in general, and ought to therefore be considered a "bad" or non-beneficial action.</p>

<p>If you know, and by "know" I mean like how you know that breathing is good and sleep is nice, what your true nature is, then you will understand on an intuitive level how to free yourself from and avoid ultimate suffering, and what is the absolute extinguishment of all suffering? :) This is the same as if you know that a fire burns from first hand experience, you call the act of sticking your hand in a fire bad, due to the effect that that will have: suffering.</p>

<p>This happens, clearly, because certain causes have certain effects. For instance, if you commit a horrible act to someone, you will eventually come to grips with the notion that this was a human, like you, vulnerable and suffering the vicissitudes of life. This will bring about the experience of suffering, and will cause you to either become numb or more sensitive. It must be contended with in some way. This is a form of suffering.</p>

<p>More so, you were suffering before you committed the act that led to further suffering. In other words, you had a feeling of suffering that acted as the motivation behind an act. That intention/motivation/feeling of suffering becomes stronger when you act on it, though we are seeking to satisfy ourselves. So it is understood that, ultimately, it is this intention that defines an act as having moral value, it is intention that creates good or bad karma, also perception, also effect. However, in Buddhism, the "aim" is to free yourself of karmic conditioned existence. It is seen that even "good" karmas are the causes of suffering, and are just a part of the truly good or truly bad trap.</p>

<p>So, are your actions set with the intention of extinguishing suffering? If so, with a correct understanding of what causes suffering, then they might be beyond karmic consequence. Are they set with the notion of true existence and value? If so, they will likely act as seeds, as cause for immediate or future suffering, and are ultimately non-beneficial towards the goal of ultimate, final liberation.</p>

<p>Question must be in the "why" of things, and have room for weather or not the apparent actor is aware of the consequences or effects of the actions that are being committed in the name of said intention. So, is there a killing where the intention was truly beyond the perception of absolute good or bad, motivated purely by compassion and free from all misapprehension and motivational suffering? I can't answer that for you, but I cannot imagine myself in a situation where a killing would not lead to more suffering. What decided that? I would argue just the bare, basic, un-elaborated, simple ole truth of our lives.</p>

<p>Remember, positive and negative are subject qualifications and are based on pleasure and pain, which are also subjective. We cannot value things in any absolute way given those truths. The universe does not judge you, you do a fine enough job doing that yourself.</p>

<p>There's a great story, and I will have to find the sutra this comes from, where a man came to the Buddha asking him to help, there was a dire situation. This man's brother (or some relative) had died, and they had not performed the necessary rights to ensure a safe passage to a heavenly afterlife, or good rebirth. He knew of the Buddha's fame as a sage and teacher, so thus sought out his expertise, certain that the great Buddha could alleviate this misfortune. </p>

<p>The Buddha instructed the man to go get two very light weight "jars", and fill one with melted churned butter, and the other with rocks, and bring them, with the body, to the river. Excited, the man did this, believing the Buddha would surely help his brother. </p>

<p>When he came back, the Buddha was waiting for him, and instructed him to place both jars in the river, and when he did so, they just floated there, slowly drifting away. The Buddha then broke open the first jar, and the butter stayed on top of the river as the jar broke. It frothed up, and was carried away. Then he broke the other jar, with the rocks, and the rocks all sank down after the jar was broken.</p>

<p>He told his new friend that there is nothing that anyone can do after the life is over. Only the weight of our good or bad deeds determine where we go in rebirth, as it does so from moment to moment in this life. </p>

<p>Our actions leave impressions in our consciousness, in our minds and on our hearts, based on our own sense of value judgements, which are based on our own sense of what is truly real and existent. These impressions carry us away, or sink us down. How is it not the case? </p>

<p>The trick is transcendence, to develop an awareness of the true nature of reality (anatta, anicca, dukkha) and get your intention fixed in a alignment with it. This is done by following the 8 fold path, and the morality section is based off of simply making it so that there are no mental distractions that will keep you from developing your awareness. As such, they are based off of non-attached, dispassionate, compassionate social activity. They are aimed at selflessness.</p>

<p>Karma is based off of volitional reactive activity to perception driven feelings, the quality of those feelings, and our relationship to them in terms of either our tolerance to them, or their influence over us. To reduce blind volitional reactivity, we can develop awareness and equanimity via meditation.</p>
 43: <p>"<em>why does that happen? What decides that killing (even if your intentions are good) will cause something negative ? What about the other actions? why does the universe act this way?</em>"</p>

<p>As some answers correctly say, an action is bad when it leads to suffering, imprisonment, and confusion - and good when it leads to peace, freedom, and correct understanding. But why? What makes an action wholesome or unwholesome?</p>

<p>The nature of suffering, imprisonment, confusion - is conflict. A mismatch between how things are and how you want them to be. A conflict between you and the world. A conflict between people. An inner conflict in one's psyche. </p>

<p>The nature of peace, freedom, truth - is no conflict, no mismatch between expectations and reality, between us and them, no inner conflict, no outer conflict.</p>

<p>So, things that lead to conflict, to division, to mismatch - are bad. And what are these things? Lies lead to mismatch between beliefs and reality, therefore lies are bad. Divisive speech leads to conflict between people. Desire leads to unsatisfied expectations, which is a form of inner conflict. Desire also leads to conflict with people who have what you want. Hatred leads to conflict. Intoxication leads to mismatch between perception and reality. That mismatch is a form of conflict. And so on. Whatever action spreads the seeds that grow as division of people, division of mind, conflict - is going to be unwholesome. </p>

<p>The same principle works for wholesome, positive action. Whatever leads to unification, to decrease of conflict, to less division, to a better match between ideas and reality, between people, and within one's own mind - that leads to harmony, to peace.</p>

<p>Truth, peace, love, acceptance, suchness - is conflictless. </p>

<p>Non-truth, war, hatred, intolerance, dukkha - is conflict.</p>

<p>Conflict and conflictlessness is the key principle behind Buddhist ethics. This is what defines whether the action is good or bad, through the mechanism of cause and effect. </p>

<p>Divisive action leads to division. Conflict-inducing action leads to conflict. Un-truthful action leads to conflict of information. Violence leads to conflict.</p>

<p>Reconciling action leads to peace. Pacifying action leads to no-conflict. </p>

<p>This is the basic principle. Conflict is bad. No conflict is good.</p>

<p>P.S.</p>

<p>The nature of suffering is conflict because mind (being an informational phenomenon) does not handle logical contradictions well. So anything that leads to an experience of clash or contradiction is perceived as suffering by the mind attached to (or identifying with) one of the sides of the contradiction. Conversely, reducing the conflict leads to experience of harmony, and that's the mechanism behind 8NP. This is already down at the level of the fundamentals; I don't think there is a further why more fundamental than this.</p>
 89: <p>In Buddhism, the concepts of good and evil do not exist as in other religions (no being is inherently good or evil). No deity tells you what to do. There are the teachings of the Buddha, that we can <em>make use of</em>, as opposed to believing in a doctrine (such as "Ithe authority tells you this, therefore you should obey*"). </p>

<p>However, there is still a distinction between the helpful and harmful, skillful and unskillful - in the context of the path (to <em>liberation, nirvāṇa, nibbāna</em>). In terms of karma (<em>actions, kamma</em>), there are the wholesome and unwholesome, but these are useful in terms of the actions we choose to avoid and to act on, in each given moment (now).</p>

<p><strong>Mara</strong>, as mentioned in the Pali Canon, is <strong><em>referred to as evil</em></strong> (in the English translation), but <em>even he will be enlightened</em> one day. In other words, noone is inherently evil (or good) - no deities, ghosts, humans or other, in Buddhism. For instance, Maha Moggallana, disciple of the Buddha, mentioned to Mara at one point that in a previous existence, he had been Mara, and (the current) <a href="http://www.accesstoinsight.org/lib/authors/hecker/wheel263.html#ch9" rel="noreferrer">Mara had been his nephew</a>. Strikingly, despite having been the "embodiment of evil in the world", a number of lifetimes later, he was one of the prominent disciples of the Buddha (Gotama).</p>

<p>An excerpt from the story: (<a href="http://www.accesstoinsight.org/lib/authors/hecker/wheel263.html#ch9" rel="noreferrer">source</a>)</p>

<blockquote>
  <p>The first Buddha appearing in our "fortunate aeon" (bhadda-kappa) with
  five Buddhas, was Kakusanda. He lived when the lifespan of man was
  40,000 years and when the first darkening of the golden age became
  evident because of a king's lack of concern and the occurrence of the
  first theft. Because of that, man's vital energy became reduced to
  half. At that time, Moggallana was Mara, chief of demons, lord of the
  lower worlds, and his name was Mara Dusi. He had a sister by name of
  Kali whose son was to become the Mara of our age. Hence Moggallana's
  own nephew was now standing in front of him at the door post. While
  being the Mara of that distant time, Moggallana had attacked a chief
  disciple of the previous Buddha by taking possession of a boy and
  making him throw a potsherd at the holy disciple's head so that blood
  was flowing. When the Buddha Kakusandha saw this, he said: "Verily,
  Mara knew no moderation here" — because even in satanic actions there
  might be moderation. Under the glance of the Perfect One the astral
  body of Mara Dusi dissolved on the spot and reappeared in the deepest
  hell. Just a moment ago he had been the overlord of all the hellish
  worlds and now he himself was one of hell's victims. A moment ago he
  had been the greatest torturer and now he himself was undergoing one
  of those terrible torments.</p>
</blockquote>

<p>Whether we believe in the details of the stories in the Pali Canon is up to each of us. However, important to note, is that we all have the ability and opportunity to choose a wiser path.</p>

<p>Regarding your questions (in shuffled order):</p>

<ul>
<li>There is <strong>no final "judge</strong>". No being (God or otherwise) controls our existence.</li>
<li>The Buddha (through long practice) awakened to (discovered, if you will) the way things are, how this existence functions.</li>
<li>Upon awakening, the first inclination of the Buddha was that "noone will ever understand this" - that it's impossible to teach. However, he was persuaded that some beings could be helped, and so he decided to teach others.</li>
<li>Briefly explained, words are inadequate to explain the way things function (karma, and so on), so instead of preaching something to believe in, the Buddha pointed the way for each of us to find out.</li>
</ul>

<p>So noone <em>"decided that killing is negative"</em> (nor did anyone decide the effects of other actions). However, Buddhists will gladly help you on the path to finding out for yourself, to discover the effects of karma (your actions). Regarding being <em>"sure we're correct"</em>, don't just take anyone's word for it. Try it out, <strong>see for yourself</strong>, do the methods and teachings from Buddhism work for you. Only then can you find certainty.</p>
