What does motivate you to down-vote a comment?
michael_nielsen: I ask whether the comment detracts substantially from the HN community?  If the answer is yes, I downvote.The nice thing about this question is that it implies many derived reasons for a downvote: being mean or insulting; egregious stupidity; being irrelevant; being "clever" without adding real value.  And so on.  I try to be careful to NOT downvote someone just because I disagree with them.