I don't see censorship as a problem in a federated system. At all. I don't see how you could.

This isn't a streetcorner, where you might be able to make a "free speech" argument. It's a private establishment where each of us are guests. It's on each of us to be respectful to our host and the host's other guests while we're in their establishment. We're here at their pleasure.

The wider free speech question: can you, at ay time, make an instance where you can say whatever you want, whenever you want? Of course you can. But likewise, nobody is ever required to ever listen to you or even hear you. Federation isn't mandatory