The hardest part of this problem lies with the relays.

We have much easier ways of client users avoiding posts they don't want via client mechanisms, like following only posts of people you follow, and not showing replies of people outside your WoT.

But keeping things off relays is harder. There needs to be active management. And I'd like to see really good tooling in this space. Does anyone know of any? I opened a NIP to standardize a REMOVE command.

Chorus relay is configured by default like the 'roach motel':  spam can get in, but it can't get out.  So if the content is illegal, at least nobody knows it is there, and you can moderate it and delete it before it is ever downloaded by anybody.  Maybe personal relays can even be the solution for new people, if they are super cheap to setup... but more probably we need open relays and active moderation.