For the site owners, the money is in flame wars and troll-fests.
I know that for the Reddits at least this was not a conscious strategy. They didn't plan for Reddit comments to get they way they are now; it was just a byproduct of growth.
Reddit could have done something about this, though. If being downmodded hurt your karma, I bet people would think twice before flaming.
It works here. I avoid flaming and trolling because I like my karma to increase. When I still read reddit, I would often troll, be overly cyncial, or generally be an ass because there was nothing to lose. (Reddit is too mainstream for there to be any intelligence there now. There is the occasional good comment from someone, but the good comments are way too hard to find.)
One other thing I should add -- reddit also punishes people who submit content. I used to seek out and post programming articles, but if you posted them at the wrong time of the day, some bot would mod them down pretty quickly. Then you would lose karma.
After a while, it becomes not-worth-the-effort to contribute to them. To summarize: reddit punishes people trying to positively contribute, and doesn't punish people trolling, flaming, and spamming. Not a good way to build community.
I've been thinking quite a bit recently on the subject of online forums; namely, why do they seem to inevitably deteriorate into a desperate, trolling flame-fest? More to the point, how can this be prevented? What can be learned from other forms of group communication, such as scientific journals?
The author makes a point that I hadn't really thought much about; namely, that observing the mayhem is itself entertaining to a large number of people, which in turn drives site owners to, at the very least unconsciously, permit nearly uncontrolled ass-hattery, in exchange for eyeballs and advertising revenue.
JoS seems to have maintained a decent signal-to-noise ratio; let's hope that Hacker News manages to do so as well.
I've noticed that forums I frequent that have high signal-to-noise ratios fall into two camps (with some overlap):
1. Niche topic. For example, I frequent forums about Go and salsa dancing that have next to zero noise. The trick I think is keeping the focus narrow: the programming reddit has worked rather well, technology-in-general forums have become cess pools.
2. Strictly moderated. It seems the only way to maintain a non-niche forum is to aggressively counteract unthinking contributions ("me too" posts, Internet memes) and trolls. Having a sanctioned area to vent and flame in, to keep the main area focused on serious (or at least on-topic) discussion may also help. The Ars Technica forums and The Straight Dope Message Board come to mind.
The dynamic on social news sites is a bit different than a traditional forum, however. Different tactics may be required to keep things in check.
Part of it's expectation setting by the core group of users.
Part of it is the same as in "Average Down" hiring. I.e., as a community grows out of the early adopters, the cluefulness/etc. of the average user will drop. A given community can only effectively support a certain rate of newbies and still be able to absorb and inculcate them into community (or drive them away :-).
"right now everybody is talking about the wisdom of crowds, and all that—which is complete horse shit, and I think the next step is realizing that what crowds pick is pretty much pornography and Internet spam, and as a result you've got to have some editing involved there somewhere."
I've been thinking that all other commenting systems suck compared to the one here. This is so nice and elegant compared to most. A little tweaking needed here or there maybe, but, aside from the unknown post links when you take too long to post, it's the best I've used.
I know that for the Reddits at least this was not a conscious strategy. They didn't plan for Reddit comments to get they way they are now; it was just a byproduct of growth.