I think the beauty of federation is that each instance can have it’s own moral code, I figure we will see everything-not-illegal-lemmy.com at some point, without any conmunity except meta ones, with admins that just do not de-federate from anything else.
You can be part of any instance that aligns with your values. And each community can decide which instance to live in. If some community wants to live in an instance which allows everything so anyone can comment, then maybe they move or start their own.
And I don’t think only horrible people would want this. I figure some community like suicide watch might want to allow everyone to comment no matter where they are from. Making de-federation the only option would suck, but it’s not. There can be different bubbles, and bubbles which contain them.
Different instances have different ideologies. You can get a user on “everything-conservative” which blocks half if the federation, or you can get into a free for all instance which allows all. Big generic instances like lemmy.world do have a big problem on their hands, they have to make the bubble the common denominator of all users, which is hard to know.