You are going to love reading this:

https://join.piefed.social/2024/06/22/piefed-features-for-growing-healthy-communities/

It's nowhere close to what you asked for, but I think you'll find that "in spirit" it leads to the same end. i.e., PieFed penalizes people who downvote all the time, and then labels their accounts, visible to everyone else (on PieFed). It does not block anything but labels them as someone who does such. It also alters the counting of votes (again, solely within PieFed though - these aren't sent out to the wider Fediverse) to prioritize the ones from people who have more upvoted content than downvoted, i.e. people with higher reputation. Anyway it's fascinating that people are investing effort into thinking about such matters.:-)

But if you truly don't want downvotes at all, then there are instances that have disabled them, e.g. https://reddthat.com/.

Alternatively, if you want to block only tankies, there are indeed ways. e.g. Lemmy.cafe and quokk.au have both defederated entirely from the big 3, so they will never see your content in the first place. PieFed has defederated from two, and I routinely see my content having downvotes visible from other instances but my content when viewed from PieFed.social has no downvotes at all (the same as any other Lemmy instance that would have defederated them).

Though if you just want to hide content from them, that's significantly harder to do but not impossible: https://piefed.social/post/307636.

As for "moronic content", that's just a feature of social media altogether (https://medium.com/@max.p.schlienger/the-cargo-cult-of-the-ennui-engine-890c541cebcb). We all would do better to pay attention to that. In some sense, it is extremely difficult to avoid though - see e.g. the recent USA election - but on the other hand, if you curate carefully where you send your content, then you may get better reception.

The thing is, you can do whatever you want... but so too can they. But we don't have to put up with their actions - we can do better.:-)