Using something like PeerTube is potentially even worse because let's say you unknowingly open a video where someone in it looks of age but technically isn't. You as a user help propagate that content while you have it open. You're not just downloading illegal content at that point. You're actively sharing it to new people.

A single instance is not federated by itself. It requires multiple instances to be considered a federation.

Just a little nitpick.

Legal yeah, but it doesn't stop ... thousands? tens of thousands? of random porn sites. There's no shortage of community driven porn at the moment. Federated solutions only seem to pop up when there's sufficient non-legal censorship of community-driven content.