It makes instance selection very important to the user (which is already a major friction point). And causes terrible UX when users can't figure out why content is unavailable to them.

It can also be used as a weapon by powerhungry admins to force centralization around their instance.

I know there aren't really great alternatives to defederation for content moderation right now. But I think that these could easily be implemented. For example, instances could maintain a 'blocklist' which users could automatically be subscribed to upon joining, but they would be able to inspect and 'opt-out' from blocking certain instances or categories if they desired.

I think this is a good balance of protecting users, and also respecting their freedom.

Keep in mind that this doesn't mean they could POST rule breaking content. (They are still users of your instance after all). Just that they would have the choice of which content they feel comfortable with VIEWING.

When all you have is a hammer, every problem looks like a nail. And defederation is a nuclear powered sledgehammer lol.