Actually I find that harsh comments are more common among children and noobs than adults and experts. A random fan watching a football game in a bar is far more likely to use harsh language about a player who misses a pass than another professional football player would.
What's happened here is itself evidence of this trend. The comments haven't gotten more negative because we were all a bunch of fools initially, and now the real experts have arrived; rather the opposite.
Half of the benefit would be from filtering out people who aren't really invested in the community. The other half would be from making people think about the magnitude of their own contributions before they criticize someone elses.
I know how much I've learned and how grateful I am for having the chance to learn from this community, I'm sure there are many others as well that feel the same.
So to the community as a whole thank you for the chance to learn until I've mustered up the courage to take the plunge.
While we can probably mostly agree that sniping (especially personal attacks) are rotten, I suspect useful insights, that are critical in nature, often get thrown in with the dirty laundry, and labelled as "negative". "Awesome site dude!! SO happy for you :) :)" and a whole bunch of potentially fake, shiny superlatives can also become a turnoff.
Quite likely this is a minority viewpoint.