But in practice small instances are better at this than large platforms, and in practice flexible moderation policies are pretty observably better at curbing abuse than ridged ones are. The point isn't that Mastadon is perfect, it's that it's
better. In business, better is good enough.
A lot of people are OK with a middle ground where moderators remain, but are closely associated with their communities to reduce communication problems and increase their stake in doing a good job. Is it really crazy to believe that someone might want to trust other people, but also want to have more selection over who they trust?
You're here, so I would hazard a guess that you're OK with that middle ground too. HN admins could theoretically turn this site into 4Chan or Reddit if they wanted to. But we both trust them not to, and the fact that they theoretically have the power is not enough to make either of us throw up our hands and say, "well there's no difference, and nobody will care, and there's no reason for anybody post on HN instead of Reddit."
There are a lot of people here posting on a dedicated tech-community Reddit clone about why fringe Twitter is a bad idea.