Disagreeing with down-voting and not commenting is poisonous, because it doesn't encourage further debate, where positions can be elaborated and facts made clear.

I've only had a few instances of down-vote spirals without refuting arguments, but I tell you, it feels like crap. I'm very likely to even change my mind regarding a subject when somebody is kind enough to present their point of view, even if they down-vote my comment along the way.

I feel HN is a very constructive environment most of the time, but sadly I'm beginning to keep my opinion to myself in threads with high-fanboy presence, where the damnation of subjective anonymous down-votes sometimes makes it feel more like 4chan.