> A good downvote is when a post/comment is abusive or pointless. A bad downvote is when the voter disagrees with the opinion expressed.
A downvote is also justified when a comment is misleading, contains a fallacious argument, or misrepresents contents of other comments or the article. Sometimes even when it's just incorrect. Unless the particular misconception is somewhat popular or difficult to spot.
Basically, anything that could be removed without loss of value, should be downvoted.
My only disagreement with this comes in when some kind of censorship is enacted once you pass a certain number of down votes. And no, the fact that you can disable that censorship doesn't ameliorate the issue - the majority will still be unable to see the comment. Reddit is particularly bad at this, as once you hit -2, your comment might as well have never been posted. Any idiot with a bot and a grudge can make anything you do invisible.
FWIW I like the way HN has chosen to handle this. You can't even downvote until you go past a certain karma threshold (eliminates sock puppetry and calling for backup), and even if you are down voted into oblivion, your words are still visible (if a little harder to see).
Now if they'd just lighten up on the hell bans. I've seen a number of valid comments here which were dead on arrival.
A downvote is also justified when a comment is misleading, contains a fallacious argument, or misrepresents contents of other comments or the article. Sometimes even when it's just incorrect. Unless the particular misconception is somewhat popular or difficult to spot.
Basically, anything that could be removed without loss of value, should be downvoted.