I'm personally of the belief that network effects have granted Twitter a relatively unassailable cultural position, or at least enough of a moat to greatly reduce competitive pressures, and so should be subjected to different standards than a local bar or paper -- and if the analogy is to a newspaper, then Twitter should be treated as a publisher with all the attendant regulatory baggage that carries. It's hard for them to argue they have a right, as a private company, to shape the conversation, and in the same breath claim they're shielded from legal responsibility for what takes place on their site.
It's definitely a tricky debate, but in my personal value stack I place individuals' freedom of speech much higher than a private company's right to refuse service, so that's where I fall.
Hard to say... there are massive network effects, but switching costs are also pretty low. Facebook seemed pretty solid not so long ago.
It's tricky because these platforms are huge, and are a public square in many ways. But they are also companies. The local newspaper is not required to print some anti-semitic screed. A local bar can kick out nazis. People do have alternative ways of freely expressing themselves.
Due to the massive size of these platforms, it feels a bit different, though in that being removed from one could really alter your online presence.
I don't have all the answers. And I suspect that Elon Musk does not, either, but we will have to wait and see...