Have you considered sock puppets? It's not out of the question to handle with human mods but detecting them automatically is pretty bad if someone is supplying credentials to each one, and sometimes it does take months or years to notice that new user Y is banned user X.

I think sockpuppets are only useful in a community with non-text signals like upvotes and downvotes or likes. These kinds of signals are not necessary and often plain corrosive to small communities. In a larger community they're a great feedback mechanism, but large communities are fundamentally different spaces than small ones and need a fundamentally different moderation approach IMO.