Well I don't know about hacker news, but there is a study that says anger is the most viral feeling in social media, e.g. twitter.

http://arxiv.org/pdf/1309.2402v1.pdf

Interesting observation, do you have a source for that?

Well, just anecdotally, blunt or angry contrarian responses seem to be downvoted in most online communities.

The key there is "contrarian".

If I posted an angry, but seemingly well-supported rant aligned with the sentiment of a particular group, people will probably upvote/reblog it (see: Trump).