There's nothing wrong with disagreeing with something, but I think it's important to provide useful feedback and even more important to provide it in a useful way.

I quite like seeing what the new hotness is, and I equally like reading about unpopular languages/projects too. I usually get more insight into those projects when I read through comments because a lot of smart people (probably a lot smarter than me) provide some awesome input. The posts that I see as having been flagged or down voted is usually because the comment was aggressive or completely non-constructive (trolling).

Personally, I'm indifferent in either case. If I don't like or necessarily agree with something I read, or it really doesn't add anything to the discussion, I just scroll down to the next comment. But I'm sure the people who are passionate enough to down vote a particular comment are the same people who will upvote others, and given the broad userbase HN attracts I'd assume that for a person who down votes a comment, there's probably another who upvotes - unless the comment is just a straight up troll then the community usually does a good job at moderating.

I think the up/down voting system works pretty well; it gives the community some ability to moderate a thread so that we can focus on the content that matters. That's not always the case of course, but I think it works most of the time.