Ok, I get that we don't want people down-voting indiscriminately - or because the guy being down-voted was rude about an answer someone gave - or any one of a hundred other invalid reasons for a down-vote.
But occasionally I see anwers to questions that are mis-leading, teach bad-practices, or are just plain wrong. And I'm becoming more and more inclined to not down-vote them. I even got a comment on a comment the other day asking why I didn't downvote if I felt that way. And it's rare, when I do downvote, for anyone else to downvote as well, presumably because someone else already has so why should they waste their reputation.
Some of the reasons given here are about wanting to encourage upvoting rather than downvoting. Funny, I thought this website was a technical resource, not a mutual back-slapping club.
Why can't we have a simple, reputation-based mechanism for rewarding good downvoting? How about the first person to downvote gets penalised 2 reputation, and the next guy to downvote gets penalised 1. But if, say, 4 people in total downvote then clearly they were right to downvote, so remove the penalty.
There have been times when people have upvoted a question I downvoted. I disagree with that obviously, but this is a community. So maybe instead of removing the downvote penalty if 4 people downvote, it should be to remove the downvote penalty if the total vote is -4 or worse.
As a programmer, I can't see that the impact of this solution on the system would be particularly huge. And the result would be to encourage people to downvote on questions which are so bad that others would be likely to support that decision. Resulting in a website where bad questions are marked as such as clearly as good answers are marked as good. Hopefully.