Now imagine if all troll threads could become just as productive.
http://imgs.xkcd.com/comics/constructive.png
(I found this hilarious, and relevant, hopefully appropriate.)
I've always loved the Karma system in all of its forms. While it may not be a sure fire solution, I really can't see it having a detrimental effect. However it is quite a bit of work to implement the infrastructure and have users adapt to it, I guess it's up to the admins to decide if the payoff would be worth it.
I actually don't think this forum is all that bad in terms of misbehavior. I've emerged scarred from the deepest recess of the interwebz, and DL has a relatively high level of tolerance and intelligence. But most sites with aforementioned system have been, overall, better in almost every respect.
If a reward system is implemented, it'll be up to the users themselves to make it really work. I mean, if the community, on average needs to clean themselves up a bit, then it has to be their decision to do that, a simple "Be better people" doesn't actually work, as much as we would like it to.