It's easy to act viciously when you're only identified by a username, and this lack of identification, I think, breeds contempt. Though it's possible to dig deeper and find out more about each commenter, while skimming comments on an article, I don't "see" a collection of accomplished human beings having a conversation. At a glance, I don't know whether I'm talking to a bunch of snarky twelve year-old know-it-alls or founders with a wealth of real-world experience. To me, this matters.
I wonder whether there are simple ways to shift the tone of the HN community - for example, by assigning a short byline to each username that gives an indication as to who the user actually is, and why I should care about what they have to say (the "about" field already exists, but maybe it needs to be brought front-and-centre somehow).
Again, I've jumped into the HN community late, so perhaps I'm being a little naive. However, maybe a newcomer's perspective could be helpful.