I agree with the OP, the level of negativity on HN is striking, if you peruse through the articles on the first page on any given day at least half will have some negative "hater" comment as the one with the most votes. You saw the same type of negative behavior on Techcrunch before they transitioned over to the Facebook commenting system, maybe there's something about anonymity that brings out the worst in people.
I think this goes hand in hand with the decrease in front-page quality. It has become normal to see a link-bait title voted to the top...and then the first ten comments lamenting about how horribly linkbaity the title/article is.
A lot of the times the article is only tangentially related to the sensationalist title and this irks a lot of people.
