Fediverse

Do we expect every single user to assess all of the toxic communities

No, I want users to have access to a list of pre-curated communities and let them customize it to their liking, like what Fediverser does.

In the same way that defederation is an admin-level decision impacting all of the userbase

Defederation is a bad way to manage conflict. It is a nuclear option that should be taken only when the offending instance (as a whole) is malicious. To stretch this "my server, my rules" philosophy further is bad design.

Good admins are like good janitors. They are not there to enforce behavior top-down.