I get the impression that this is supported by hn to some extent by the "don't comment with me-too, or cool-stuff" kind of rules. If you see something that's actually new to you, you'll usually have a response like: this is good (up vote), disagree (comment), know something more (informative comment), know something related / similar (start slightly off-topic but related comment thread). And these are all useful comments to some extent.

If it's really news to you, the comment is really unlikely to be informative or deep. Actually there are people who are almost always in disagreement with news on some topic, but I don't think they're bad (see tptacek on every homemade-crypto related article).

I think the general negative response is just a result of the news themselves. Before you really get to understand/apply/have fun with some of the stuff, it will be far away from the front page already. But as long as there's at least a bit of constructive criticism in the negative ones, I think I'm fine with it.