I agree that you raised some valid points but I think your delivery in making those points were pretty abrasive though. At least that's how I interpreted it!
every social community I've seen eventually has to give up the downvote as a tool and just have upvotes or likes, or else they peak when the downvoting gets out of hand. I think HNN passed that point about 1-2 years ago. I see more and more worthwhile comments greyed out and I'm sure good contributers who advocate unpopular languages or discount the latest hotness are now driven away.
I think the HN community is pretty diverse and for the most part attracts people who are genuinely interested in constructive discussions. The folks who blindly dismiss something as being the new "hotness" are probably down voted because they were simply doing that - blindly dismissing without providing any useful feedback.
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.