I don't down-vote for disagreement. I down-vote for comments that I think are seriously detrimental to the goal of maintaining high signal-to-noise in HN. For

I don't down-vote for disagreement. I down-vote for comments that I think are seriously detrimental to the goal of maintaining high signal-to-noise in HN. For example, imagine a comment that just said "LOL!". Yes, I would downvote that, and it says "Please don't make empty comments like that. If you like it, upvote it, and be done with it". I also downvote for flagrant wrongness, and I mean really mean flagrant. For example say there was a post on geolocation and somebody insisted in all seriousness that the Earth is flat. I would downvote that for the obvious reason. That said, I think the general guidelines do not frown on voting for disagreement and many people do. I don't know for sure, but I suspect I downvote once for every 50 upvotes or something of that order - it's pretty rare.