You are just saying that physical life doesn't function. People get banned or removed from all sorts of informal and formal groups all the time because of completely illegitimate reasons. That's just human politics embedded so deeply in our psychology it will never go away. They simply move to different groups - and similarly online they can move to a different federated server.

But that's not possible in today's oligopoly of social media. An invisible algorithm will ban you, and there is no way back, and few alternates. Big Social Media is way worse from a sanitizing perspective than some federated social media.

I have no deep problem with exclusion; as you say, that’s human nature and unfixable. Making mods personally legally liable for everything that appears on their board is just insane. How many minutes are acceptable for them to see and review content? Or does everything have to be pre-approved?

I know a local blog that pre-approves every comment. He lets a lot of stuff through, because he lets people be dumbasses. If he were personally liable, the conversation would get a lot quieter.