I dont have much to add other than I am an experienced admin and was dismayed at how vulnerable Lemmy is. Having an option to have open registrations with no checks is not great. No serious platform would allow that.
I dont know of a bulletproof way to weed put the bad actors, but a voting system that Lemmy can leverage, with a minimum reputation in order to stay federated might work. This would require some changes that I'm not sure the devs can or would make. Without any protection in place, people will get frustrated and abandon Lemmy. I would.
If you figure it out, let me know. I've created a couple communities that I liked from Reddit, but nothing. I believe people are just sticking to the top 5 instances and that's it. Kind of defeates the purpose of the fediverse. If lemmy.world went down, that would take half of the lemmy users with it.