I’ve thought about building a truly decentralized app similar to lemmy, but the question if how to prevent things like CSAM from ending up on unwitting users’ devices is the main thing stopping me.

Lemmy has exactly the same problem, and the solution seems to be to defederate from instances that host that kind of content. That works, but it’s a lot of work for an admin, so we absolutely need better moderation tools to help detect unwanted content and block the source of it.

I just wish people wouldn’t post such nonsense.