My position is that downvotes should not exist. There are three ways to view posts and comments:
A. you agree with it, and appreciate it, so you upvote it to give it more visibility because that is how this whole system works - popular stuff should rise to the top, and an upvote is a measure of popularity. If you see popular stuff but have something to add, you will usually upvote and comment on it.
B. a comment or post is a violation of site rules, and should be reported. You flag these and leave it up to moderators to deal with it.
C. you disagree with a comment or submission. If you are given a downvote button, people will often just downvote the stuff they do not like and leave it at that. But that is antithesis to discussion, and it is a very real problem on reddit, where users often use downvotes as a substitution to real debate or testing ones beliefs or knowledge. The correct answer is to reply why you dislike a comment, and try to start a discussion on it. If it is not violating site rules (and trolling can be, depending on site, one of those rules) then it is your duty to inform the poster why they are wrong.
Downvoting is a cop out to take the truly controversial topics that make for the better discussions out of consideration, and that is why you get an echo chamber - when you only have upvotes, if there are three opinions, then those three will be ranked by popularity. If you have downvotes, only the most popular opinion will ever show up because not only is it upvoted the most but the other two are downvoted off the site and those with dissenting beliefs just leave. And then you end up with the echo chamber and no real discussion left.
I think that is why HN gets higher quality, in the general case, than most subreddits around technology. They have downvote buttons that naturally turn their communities into hive minds, whereas here you have to actually contribute a bit to get that power. I'd rather see it removed entirely, tbh.