My experience has been the the opposite, I stopped contributing to user forum based sites after I left /. and did not do so for a long time. I read HN for a while before deciding that it was home, and it was, because in my perception, there was a lot less "I'm the smartest guy in the room" conversations. Take that with a grain of salt though, because it has been a long long time since I have been over there. Things almost assuredly have changed since then. Has anyone else had the same positive impression of the exchanges over there? Most the posts I see on the subject tend to complain that there is still a lot of it going on.
A good example is this post from several weeks ago on the subject of denying blood donations from donors with a history of male-to-male sexual contact: http://news.ycombinator.com/item?id=3237895 It's very fact-centric, to the exclusion of any sort of pandering or apology. When I read this post several weeks ago, I immediately thought, "this would never fly on reddit; people would quickly downvote it for being 'insensitive' or similar."
This also reminded me of PG's essay "Persuade xor Discover." http://www.paulgraham.com/discover.html HN users seem to care less about "persuasion," which can lead to perceptions of "unfriendliness" because things aren't written to please people. However, it does lead to a lot of interesting discussion that couldn't take place on a site more concerned with being "nice."
E.g. I don't think I've ever been downvoted on slashdot but if I did it would be for spam or hate, not a "thanks."
On the flip side I can see where legitimate comments getting down-voted could be taken as rude, the ones I hate to see are new people asking legitimate questions and then getting dog-pilled into oblivion, but it is the nature of the site. I do wish there where less of the i don't agree, or my comfort does not like what you say down-votes but for me it is preferable to the "i'm always right" personality. I never really thought about viewing down-votes as rude, save for the occasions where it is evident that it is a group think dog-pile.