I seem to have run into my karma limit, downvoting. I really don't like the way this system works. I upvote more than I downvote so I don't think I'm being exceedingly negative. If I want to apply a fairly reasonable level of quality control the system quickly stops me from doing so, leaving me to either stop that quality control, or not apply the same level of discernment to my own comment posting, in order to gain more karma. It seems a rather perverse incentive.
It also means that downvoting doesn't just signal that a comment is bad/too highly ranked, which is what I've been using it to do; it also reduces a commenter's ability to help filter and rank comments by quality, even though that's often easier than making a high-quality comment and even though my reasons for downvoting don't always reflect strongly on my general opinion of a user.
Edit: I'll assume losing karma doesn't cancel any downvotes I've already cast, although it makes me slightly worried.
Edit 7/10: In naive terms, every time I downvote a bad post I might be effectively upvoting four other equally bad posts.
Downvote buttons seem to have just stopped working for me, saying I need at least 1 karma. I'm posting in case it leads someone to fix the problem.