I'm not defending these hypothetical Fediverse apps that don't moderate. I'm saying that compared to Fediverse apps exposing a few thousand people to hate speech, Facebook and Twitter actively promoting bigotry, propaganda and conspiracy theories to tens or hundreds of millions of people is far more harmful — even if they make a nominal effort to prevent it from happening.

And, more to the point, I'm alleging that the reason Google is taking down the Fediverse apps and not Facebook or Twitter has nothing to do with their moderation policies, and everything to do with money.

Other than that, the instances themselves simply choose not to federate with questionable instances. This happens in an almost organic way where if an instance refuses to block federation with another questionable instance, other instances will then also refuse to federate with that instance.

The result is a network where hate-speech and undesirable content has been almost organically filtered out.

But keep in mind that the (client) apps themselves are more like web browsers. Anyone can host their own website and access its content through one of these apps. This also means that instances which are blocked by an app can very easily circumvent that as well.

(Sorry for my bad english and repeatedly using the word "instances")

Twitter actually hosts the trashpile, they're more responsible for it than some app that just lets you access trashpiles on third party servers.