How is it not censorship if you are making the decision for not only yourself, but others, too? It sounds like saying bleeping swear words on TV isn't censorship because you just don't want to hear bad language.

People are choosing to be on instances which block certain things. That's their choice. I want to be able to have a conversation without filling it with racist screaming. Choosing to be in places that don't allow that is my choice.

If I refuse Nazis access to my house and other people chose to visit my house knowing I won't let Nazis in, I'm not censoring Nazis as I have no influence on their freedom of speech - they remain entirely free to speak elsewhere, to people who are willing to listen. I have no power to stop them from speaking, just to offer those who don't want to listen somewhere where they won't have to.

Nobody is forced to join a Mastodon instance that censors Nazis - there are many that don't, or you can run your own.