There’s some misinformation floating around regarding Lemmy not having a karma system. While many have discovered otherwise, this is for those who may not have.
While it’s not exposed in the Lemmy default user interface, Lemmy does have a fully functional karma system and it is visible in third party clients such as WefWef and Memmy.
Do with that what you will.
I think downvote rationing could work, possibly. It is only an issue for subs that are focused on discussion of divisive topics… downvotes work fine for most communities