Which authority dictates/regulates that in computer science a journal paper cannot be presented in a conference? I was taught that conference papers in computer science count as publications. Therefore, a journal paper cannot be presented in a conference because of plagiarism reasons, and vice versa. 

I confirmed this information:


Publishing the same results at multiple conferences
Submitting the same research to multiple conferences
Journal publication and acceptance to competitive conferences
Under what circumstances can one republish a conference paper/presentation?
Present journal paper at conference or the same work at multiple conferences


The weird part for me is understanding which authority (IEEE?, ACM?) regulates this? Is there any document that support this? It seem that this policy in CS emerged from the community (bottom-up; see for example this) – sort of like hand shaking or bowing in Japan – and is therefore self-regulated by people. 

Related to this question (EDIT: I will ask them separatedly later as suggested in the comments but I feel I need to clarify certain issues I seem to be confused with):


I have had multiple arguments with colleagues of other fields
that disagree with me in that conferences papers/presentations don't 
count  as  publications (I am in a multidisciplinary field). I feel I
tend to loss these argumentations because it is one CS student against
the rest. In a way, it would be easier if I could refer people to some
authority.
If I simply don’t want to follow the rule for conferences that 
apparently don't count papers as publications, what are the real
consequences apart from the social lynching? To be clear, the work is
done but not published - just somehow presented in a conference (*).
Is there any way to confirm that a conference or proceeding is formally
registered as an (or to an) editorial/publisher?
Is there any other way of presenting published results in a
conference as, for example, simply abstracts (*)?


(*) In some areas people just present abstracts, and depending on the area, the conference accepts almost everything. The main goal of this seems to be networking - presenting the work and having the opportunity to interact with people that assist to your presentation (if any).
As is, a journal paper cannot be presented in a conference in many fields, not only in computer science, whether the conferences are counted as publications or not. Of course, you can always present an improved version of a previous work, if the improvement is significant.


  It seem that this policy in CS emerged from the community (bottom-up) (e.g. see this), sort of hand shaking or bowing in Japan - and therefore self regulated by people.


The entire academic world is somehow self-regulated by people, and most people agree on the fact that trying to resell the same paper twice is unethical because it can lead to an artificial inflation of the number of publications, which is one of the many indicators employed to hire people in academia. 

And even if you don't find that unethical, you don't want to read the same publication again and again, do you?