I have a difference of opinion on the matter of downvotes. A long time ago I decided to try to treat downvotes on my own posts as editorial feedback. In the best case, it just meant I was unclear. In the worst, case I said something stupid. In between there are cases where I knowingly wrote something likely to get downvotes.

I believe downvoting a comment that I disagree with is often far better for HN than expressing my passionate "well informed" opinion. Downvoting prevents my inclination toward "trolling lite" in the form of explaining how someone is obviously wrong for the sake of correcting the internet.

To put it another way, downvotes are for downvoting. Downvoting and moving on is the right choice whenever it proxies the possibility of worse behavior. A downvote can be a way of mocking out a flamewar or general meanness.