I usually only downvote purely out of disagreement if the person trotted out some argument that everyone who disagrees with them has heard before, so that I don

I usually only downvote purely out of disagreement if the person trotted out some argument that everyone who disagrees with them has heard before, so that I don't leave the response everyone already knows that rebuts it. E.g., the old pro-/anti-GPL debate. Downvoting lets you get satisfaction without dignifying a dumb thread with a response. Also I downvote things that are just conversational, low content, inflammatory. But I don't downvote a lot, only when the comments seem to be derailing things.