This site is not in a state of nature. There are all kinds of things I do to keep meanness at bay, and the situation would be a lot worse if I didn't. Preventing the site from declining into a swamp of meanness and stupidity (I believe the two are closely related) is something I think about constantly.
Does that imply anything regarding hateful posts in HN, or is it just a 'hey, there's a correlation here' observation?
Or as the saying goes "Never argue with an idiot. They will drag you down to their level and beat you with experience."
An overly civil debate climate, viewed as a "circle jerk", might also keep some valuable contributors away. Whether that is a good thing or not is up for debate of some sort.
A rational person is capable and willing to change their mind when new evidence is offered.
A irrational person may easily change their mind on some topics with no evidence and never change their mind on other topics(politics/religion/etc) even with the best evidence.
Everybody knows that crazy talk is a waste of everyone's time. I get depressed every time I find myself reading the comments on CNN or YouTube. . . .
Unfortunately this is often the case, however it should still be possible to make some sort of judgment based on rationality, patience, and communication skills of the people involved in a debate. If one side is constantly irrational and/or impatient then they are often also described as mean-spirited. This is why comments/complaints like the op's can be valid and important; though (ir)rationality/(im)patient/lacking communication skills are my preferred terminology over "mean-spirted" and other similar descriptions.
Really, I kind of get tired of reading stuff like this because there is always some subtext to it. "mean-spirited" usually means, "someone disagreed with me". If people disagree with you, you can either get over it or learn to argue better. Passive aggressive, "oh noes everyone is so mean" is not going to change what people think. Good writing will.