The recent implementation of a -5 karma penalty for replying to comments that are at -3 or below has clearly met with some disagreement and controversy. See http://lesswrong.com/r/discussion/lw/eb9/meta_karma_for_last_30_days/7aon . However, at the same time, it seems that Eliezer's observation that trolling and related problems have over time gotten worse here may be correct. It may be that this an inevitable consequence of growth, but it may be that it can be handled or reduced with some solution or set of solutions. I'm starting this discussion thread for people to propose possible solutions. To minimize anchoring bias and related problems, I'm not going to include my ideas in this header but in a comment below. People should think about the problem before reading proposed solutions (again to minimize anchoring issues).
There's probably a corollary to Löb's theorem that says a community of rationalists can't add new members to the community and guarantee that it remains a rational community indefinitely. Karma from ratings is probably an especially poor way to indicate a judgement of rationality because it's also used to signal interest in humor (to the point that slashdot doesn't even grant karma for Funny moderations), eloquence, storytelling, and other non-rational things. Any karma-increasing behavior will be reinforced and gain even more karma, and the most efficient ways of obtaining karma will prosper contrary to the goal of creating high quality content. Does every user with more than 1000 karma understand that concept sufficiently to never allow a user who does not understand it to reach 1000 karma?
To be honest I didn't fully grasp the concept until just now. I was ready to start talking economics with karma as the currency until I realized that economics can not solve the problem.