Remember that a person’s name is to that person the sweetest and most important sound in any language. -Dale Carnegie
Although the name "John" is less popular now, when I was growing up John was the most popular name. Many of my friends were also named John. People would sometimes ask us: what do you want to be called? And the answer was, we kind of figured it out on our own. There didn't need to be a system. Sometimes I was called "Borwick;" sometimes I was "John" or "John B."
In my informal emails, I call myself "John B." "John B" is also the name I give to restaurants and coffee shops. I just like being called "John B"–I think it's less formal and also clearer in the event of multiple Johns. Occasionally the restaurant will just write down "John" but usually they'll write down "John B."
I think people should be able to choose their own names, and that others should call them by that name. Using a person's name is a sign of respect. People who don't call the person by their name, or who insist on using a previous name, are jerks. In high school, someone who went to my school had decided ahead of time that they wanted to use a new name, and that's the name everyone called them. It wasn't a big deal except to a few people who tried to make it into a big deal.
I think people have the right to define their name, be it Ƭ̵̬̊ or John or the Doctor or anything else. I think people should be able to change their names multiple times, informally and legally, so long as there's still a way to trace a person's names/past through the legal system. I find it almost stranger that kids have no say in their initial name.
The EU-GDPR's approach to data privacy is that people own their data, rather than companies. I think names are like that: a name is the person's property, and they have the right to control how it's used.
I don't know that it's worth engaging with why jerks might not respect a person's name. If I were to try and empathize with these people, I feel like the main argument against letting people change their names is the slippery slope argument: if we let people change their names, what if they change their names to something vulgar or something deceptive or otherwise something not "desirable." I just think that people will figure it out–there doesn't need to be too much formality around rules and what people can be named.
Another way of saying all this is, "you do you." Let people do what they want to do–it's not hurting anybody else. I believe in freedom to be you rather than freedom from offense.