I wonder if Stack Exchange has considered some mechanism to limit those who primarily downvote, or at least downvote much more than they upvote?
As already transpired in comments the proposal was made, by Jeff Atwood himself, and rejected: Should we have a policy about "too much downvoting"?
I would not have liked that particular proposal either, with a global ratio-restriction. However, I think I could get behind something roughly like we have for question and answer voting, that is, one gets extra votes if one votes in a somewhat balanced way.
Personally, I would not discriminate on type (up/down) but make it symmetric (but this could be discussed), say:
a user has 30 votes/day yet in addition they can cast up to 10 extra votes as long as there are not more than 30 of the same type (up/down).
This is not fully thought out as one would have to think about the interaction with the 10 extra votes that exist for questions. One could also think about the exact numbers. I mainly meant to bring up the idea of a milder and more symmetric steering mechanism.