user92394: The bitcoin is by many people believed to be used as a method of payment, just like fiat currencies, in the future. Apart from the other big use case of a stable store of value.
But the payment use case is very flawed currently. because from the day someone starts to make a payment and shows her public key around, everyone (also people who have malicious ideas) could start to track this person based on her public key for the rest of her live basically on the blockchain. Everyone using btc payments would be sitting "naked in a cup made of glass".
This is horror scenario for all, companies, private persons, a dangerous inherent feature.
this is currently not possible with cash or bank transfers. everyone can have your IBAN accout number, but no other person who has your IBAN (and is not a bank employee) can ever track you or know about your financial state, etc.
How can btc in such grave circumstances achieve mass usage status as payment method??  Is privacy not needed as prerequisite for payment use case?
How are bitcoin devs trying to tackle this unsolved issue? Or do you think this is not an important issue.
Thanks

user63872: Bitcoins themselves are fungible, and addresses are designed to be for one-time-use only. It really comes down to how you use it, and it is entirely possible to transact using Bitcoin in a private manner. 
If the user is naive and has poor practices, then it is possible to track their financial history.
But if the user is smart and uses best practices (no address reuse, coinjoin/payjoin transactions, lightning network, etc), then they can enjoy a very high degree of privacy, and sovereignty (you don't get this with traditional banking). 
This article is a great writeup about privacy while using Bitcoin.

user13866: 
How can [Bitcoin] ...achieve mass usage status as payment method?

I suspect much research has been done in this area. Privacy is an important obstacle but not the only one.

Motivations and Barriers for End-User Adoption of Bitcoin as Digital Currency. Presthus and O'Malley, 2017

The largest group, the non-users, state that they are awaiting for others to start using bitcoin, as they question the value and security issues. We conclude that we may witness a deadlock where “everybody waits for everybody”


Cryptocurrencies: Overcoming Barriers to Trust and Adoption. Gurgec and Knottenbelt. 2018

A number of challenges remain to cryptocurrencies becoming more widely adopted as a method of payment. Many of these challenges are linked to the underlying technology but also include legal, economic and social factors.

...

More specifically, the 6 issues listed below and discussed in detail throughout the report, hold the key to the adoption process and improving trust:  

Scalability
Privacy
Volatility
Regulation
Incentives
Usability/Design thinking



Top Ten Obstacles along Distributed Ledgers’ Path to Adoption. Meiklejohn. 2017.


Scalability: do we need full agreement?
Privacy: how to protect data?
Cost-effectiveness: what is the cheapest way?
Scalability: why store every transaction?
Interoperability: how to talk to each other?
Agility: which algorithms do we use?
Key management: how to transact?
Meaningful comparisons: which is better?
Governance: who makes the rules?
Usability: why use distributed ledgers?


It is necessary to read the full document for the description of the actual problems in the above areas.

92394: <p>The bitcoin is by many people believed to be used as a method of payment, just like fiat currencies, in the future. Apart from the other big use case of a stable store of value.</p>

<p>But the payment use case is very flawed currently. because from the day someone starts to make a payment and shows her public key around, everyone (also people who have malicious ideas) could start to track this person based on her public key for the rest of her live basically on the blockchain. Everyone using btc payments would be sitting "naked in a cup made of glass".</p>

<p>This is horror scenario for all, companies, private persons, a dangerous inherent feature.</p>

<p>this is currently not possible with cash or bank transfers. everyone can have your IBAN accout number, but no other person who has your IBAN (and is not a bank employee) can ever track you or know about your financial state, etc.</p>

<p>How can btc in such grave circumstances achieve mass usage status as payment method??  Is privacy not needed as prerequisite for payment use case?</p>

<p>How are bitcoin devs trying to tackle this unsolved issue? Or do you think this is not an important issue.</p>

<p>Thanks</p>
 63872: <p>Bitcoins themselves are fungible, and addresses are designed to be for one-time-use only. It really comes down to how you use it, and it is entirely possible to transact using Bitcoin in a private manner. </p>

<p>If the user is naive and has poor practices, then it is possible to track their financial history.</p>

<p>But if the user is smart and uses best practices (no address reuse, coinjoin/payjoin transactions, lightning network, etc), then they can enjoy a very high degree of privacy, and sovereignty (you don't get this with traditional banking). </p>

<p><a href="https://en.bitcoin.it/wiki/Privacy" rel="nofollow noreferrer">This article is a great writeup about privacy while using Bitcoin.</a></p>
 13866: <blockquote>
  <p>How can [Bitcoin] ...achieve mass usage status as payment method?</p>
</blockquote>

<p>I suspect much research has been done in this area. Privacy is an important obstacle but not the only one.</p>

<hr>

<h1><em><a href="https://www.sciencedirect.com/science/article/pii/S1877050917322044" rel="nofollow noreferrer">Motivations and Barriers for End-User Adoption of Bitcoin as Digital Currency. Presthus and O'Malley, 2017</a></em></h1>

<blockquote>
  <p>The largest group, the non-users, state that they are awaiting for others to start using bitcoin, as they question the value and security issues. We conclude that we may witness a deadlock where “everybody waits for everybody”</p>
</blockquote>

<hr>

<h1><em><a href="https://www.imperial.ac.uk/media/imperial-college/research-centres-and-groups/ic3re/CRYPTOCURRENCIES--OVERCOMING-BARRIERS-TO-TRUST-AND-ADOPTION.pdf" rel="nofollow noreferrer">Cryptocurrencies: Overcoming Barriers to Trust and Adoption. Gurgec and Knottenbelt. 2018</a></em></h1>

<blockquote>
  <p>A number of challenges remain to cryptocurrencies becoming more widely adopted as a method of payment. Many of these challenges are linked to the underlying technology but also include legal, economic and social factors.</p>
</blockquote>

<p>...</p>

<blockquote>
  <p>More specifically, the 6 issues listed below and discussed in detail throughout the report, hold the key to the adoption process and improving trust:  </p>
  
  <ol>
  <li>Scalability</li>
  <li>Privacy</li>
  <li>Volatility</li>
  <li>Regulation</li>
  <li>Incentives</li>
  <li>Usability/Design thinking</li>
  </ol>
</blockquote>

<hr>

<h1><em><a href="http://www0.cs.ucl.ac.uk/staff/S.Meiklejohn/files/top-ten-paper.pdf" rel="nofollow noreferrer">Top Ten Obstacles along Distributed Ledgers’ Path to Adoption. Meiklejohn. 2017</a></em>.</h1>

<blockquote>
  <ol>
  <li>Scalability: do we need full agreement?</li>
  <li>Privacy: how to protect data?</li>
  <li>Cost-effectiveness: what is the cheapest way?</li>
  <li>Scalability: why store every transaction?</li>
  <li>Interoperability: how to talk to each other?</li>
  <li>Agility: which algorithms do we use?</li>
  <li>Key management: how to transact?</li>
  <li>Meaningful comparisons: which is better?</li>
  <li>Governance: who makes the rules?</li>
  <li>Usability: why use distributed ledgers?</li>
  </ol>
</blockquote>

<p>It is necessary to read the full document for the description of the actual problems in the above areas.</p>
