The Fediverse is everything but uncensored--all popular instances have a very strong left-wing set of guidelines and will refuse to federate with you if you don't have the same guidelines.
Can you point to those guidelines on the top instances? I'm not sure which of the most popular instances prohibit, say, expression of conservative views. Though perhaps you do have a point - they might be more tolerant of far-left views than far-right views.
I also think defederation because of lax guidelines doesn't happen as often as defederation because of users of other instances behaving in ways which heavily go against the guidelines - whether it's harassment or posting porn the major instance doesn't want, etc.
Fedi, moreso than Twitter, is what you make of it, and there are many (but just not as many) users on 'lax' instances (e.g. FSE or SPC or Smug or Weeaboo.space or Gameliberty... you name it) to talk to. I have an account on a major instance, a 'lax' instance, and my own instance. I have personally found I extract the least value from the local timeline 'lax' instance.
I'm skeptical of the idea that defederation-by-association is as common as another commenter here suggests.
I don't think it's meaningful to say a newspaper is 'censored' when there's another newspaper stand right next to it that shows every paper in full.
There's massive diversity of political opinions on Fedi.
I wish the Fediverse was like that. Since I got off Twitter I've wanted to look for alternatives, but, alas...
It gets to the point where the Fediverse ends up enforcing a pretty narrowly defined orthodoxy not reflective of even many traditional anti-Nazis. For example, the Fediverse has a conspicuous numbers of strident trans activists in influential positions, and e.g. posting the sort of views that J.K. Rowling held (shared by many intellectuals who consider themselves on the Left) may to outrage and refusal to federate.