Doesn't defederating mean posts won't show up? That seems like probably the main reason to defederate. You'll never stop people from creating new accounts or a new instance, but defederating creates friction forcing people to take an alternative route if they want to troll.

Regarding lemmygrad, has there been any trolling via alt accounts on instances that have defederated? Even if I disagree with their politics they seem generally respectful of the communities. But I've been away from Lemmy for a while so maybe I've missed something.