But... I also think that the very structure leads to argument as well. Most of us have heard some variation of Cunningham's Law- "The best way to get the right answer on the Internet is not to ask a question; it's to post the wrong answer."
However, most people don't realize that this was coined in the '80s.... and was about Usenet.
I think that there are a confluence of factors- the most obvious is that people are less likely to engage to say, "You're right!" Sure, some do ... but seeing something wrong ... on the internet ... that really motivates people to actually write something. I think that this is a common experience; you see a person post something that you agree with, and you might (if it is offered) give a "like," but you are probably less motivated to say, "Snarf. I noticed that, as always, you are correct. BRAVO!"
On the other hand, when you see something wrong, you just can't help yourself.