Downvoting of this comment only makes sense to me if someone disagrees with you. And on that note, is that what downvoting on HN is for? Other link aggregators typically say downvoting isn't for disagreements; that's what commenting is for.
I've only downvoted someone once, and that was for a snarky, 5-word top-level comment that did nothing to expand the conversation - the kind of downvote that is exempt from explanation.
But then there are people who silently disagree via downvote. To that I ask what the purpose must be. "I think you're wrong" - How? Why? Is it my tone? Lack of evidence? To me, downvoting without explaining is just a smug way to feel less insecure about one's own opinions without having to stand up for anything.
I find that downvotes generally account for well below 10% of my voting, and I use them mostly to denote needed correction in tone or presentation, or repeated endorsement of a "fact" without reference after it's been asked for. Even then, I'll only do so after leaving a comment or confirming someone else has a comment that covers my reasoning for downvoting. Without some explanation, it's far to easy to assume downvotes are due to disagreement on what is all to often a subjective item, which doesn't really help the discussion at all.
A Poll on people's downvoting behavior would be interesting, but as it would be self-reporting and subjective, the results would be next to meaningless if mundane.
