See longer post (not by me) there, if all is true then they should fall under both the spam and mass lemm.ee rule breaking defederation rules, both bigotry and abusive language, though not always in combination.
Also the covenant thing Mastodon has would probably be a good idea.
What’s the big deal? This sort of thing happens frequently. That’s why you have moderation and rules.
Lemmy is a confederation of (ideally) self-moderating instances, individual instances can’t be expected to take up moderation load that should be covered by other instances – like the home instance of notorious brigaders like /r/the_donald folk.
Or, differently put: See this post by our god emperor sunaurus.
What about the moderators of the forums themselves? I would think that is the first line of defense. Instance moderators then step in if necessary, but that will only affect what happens at that instance?
This should be a safe place where we can all discuss our belief. Hateful disagreement must not be allowed.