Communities can’t be shut down, but they can be shut out. This is also just true in life in general.

If The_Donald were to set up shop on Lemmy.ml, they could ban the instance and the members, but they could just turn around and join another instance.

So, what do you do then? Site admins can ban the remote instance, and they can put pressure on the hosting site admins by threatening to defederate.

Let’s say the new hosting site’s admin gives into defederation pressure and also bans the instance and its members. We’ll, then those people can set up their own server. Now, the admin won ban them.

But none of the major servers will federated with them. They’ll be alone on their low population fashy instance (or not so low population - Truth Social is suppsoey the biggest Mastodon instance), effectively quarantined.

That’s the best anyone can do. That’s true with or without Lemmy.