This is just an insane level of censorship, I don't care if they are literally for-real Nazis. It's not the place of corporations to pick and choose who should have Freedom of Speech.
Asserting that they should not be able to do so is, in fact, an argument against freedom of speech.
Freedom of speech is not an entitlement to have other people use their resources to further your speech irrespective of their own preferences.
Getting the legal benefits of being a modern public square but then also being able to silence people to improve your profit margin is where this seems to be the problem
I don't see anything about Twitter in the 1st Amendment.