It's troll vs. troll in a fight to the death (of discourse). Spoiler: everybody loses.
Good comments can turn an OK story into a great one. Great comments can easily eclipse the post they're attached to. We're not here to talk about those.
We're here to talk about the dregs, the scum, the poison. We're here to talk about the reason most people don't read the comments, and even fewer people bother writing them.
We're here to figure out who has the worst comments on the internet.
The contenders:
Newspaper and TV Channel Sites
Why? Hahahhaa, have you ever been to the New York Post website? Look at any story about crime, particularly ones where the alleged perpetrators aren't white. This is some grim stuff — deeply angry, unequivocally unproductive 30-word conniptions by people who seem to hate everything and everyone. The problem runs so deep that even a switch to a Microsoft/Facebook-powered commenting system didn't stem the flow of vitriol.
Other sites don't fare much better. These guys have been accepting comments FOREVER, so you'd think they'd have them under control by now. But a lot of them, particularly smaller papers, are fighting an uphill battle: they cover everything, so their audiences are broad; they're often using off-the-shelf websites and comment systems, so their technology is poor; they're understaffed, so their moderation is weak; they're often writing about big national news, but anyone with any savvy is probably reading or posting somewhere else. If you're writing a comment on a local news syndication of an AP wire story about international affairs, it's safe to assume that nobody needs to hear your opinion.
As for the big TV sites, I think it's just a matter of volume. Imagine the kind of person who would go to CNN.com to "be heard". Now imagine 1,000 of those people all talking at once.
Worst offenders: NYP, any local paper, CNN
Sliver of hope: The big guys — NYT in particular — have learned to moderate comments extremely aggressively. (Read: they just delete them all.) It's not a fix, but the bandage is working pretty well.
