I've spent many hours over the past several years trying to understand and mitigate such problems. I've come up with a bunch of tweaks that worked, and I have hopes I'll be able to come up with more.

The idea I'm currently investigating, in case anyone is curious, is that votes rather than comments may be the easiest place to attack this problem. Although snarky comments themselves are the most obvious symptom, I suspect that voting is on average dumber than commenting, because it requires so much less work. So I'm going to try to see if it's possible to identify people who consistently upvote nasty comments and if so count their votes less.

It is hard to imagine that the site guidelines you write years and years and years ago when this place was tiny are, intact and without change, the optimal guidelines for the site in 2012.

It's also the case that the things you say to guide the tone of the community, for better or worse, have a huge impact on how the community works.

If it should be a norm of HN that criticisms be kept constructive, and that the community should have a default position of supporting entrepreneurship (and, more generally, of supporting attempts to build anything) --- and, that should be a norm. --- why can't you just say so? Not in comments, buried in random threads, but in somewhere prominent on the site. Like, for instance, the guidelines. Which you need to update. Please.

Actually I find that harsh comments are more common among children and noobs than adults and experts. A random fan watching a football game in a bar is far more likely to use harsh language about a player who misses a pass than another professional football player would.

What's happened here is itself evidence of this trend. The comments haven't gotten more negative because we were all a bunch of fools initially, and now the real experts have arrived; rather the opposite.