I have a few opinions on the subject which ranges from people being treated like that at work and finding a channel to 'pay back', not being able to put themselves in the other's shoes, feeling like everything is trying to sway them so they need to keep their guard up, feeling small in relation to the author and using comments to try to fill the gap.
Now fellow HNers, please tell me from your perspective, why do you think you have the tendency to criticize everything you read? Why do you think that is the best approach? Do talk to family members and colleagues the same way you talk on HN? How would you change your and other people's approach to create a growth minded environment?
Scenario 1: You see something that make a good point. You nod and move on... maybe upvote. But the result is that good points are quiet threads, and don't fill up the site with huge discussion because they simply made a point and left it at that.
Scenario 2: "Someone is wrong on the internet!" Downvote! Argue. Get upvotes for proving someone wrong. Busy threads, with higher emotion.
I don't think people come to HN to deliberately argue and criticize. But argumentative threads get more heated, are longer, and take up more of the discussions, and thereby have high visibility.
My personal approach it that I mostly only read the top 1-2 levels of any thread, and try to not go down negative rabbit holes.