It’s a difficult balance. A block feature that influenced ability to downvote would essentially render all downvotes useless. The best solution I can think of is a very sophisticated rep system that has less influence over upvotes but a big influence on the weight of downvote. It could identity potentially connected accounts through behavior and reduce downvoting ability on someone who is bullying the same person all the time without a variety of other people also downvoting.

Perhaps people could be voted on their downvoting behavior and it effects their rep and people with low rep have little downvoting power.

I think ideally you don’t want to make downvotes stronger when they come from more diverse users with wider connections to different groups of users. Sounds like it’d be a pretty difficult project but maybe someone could do it.