When you think of discussion forum design as a security issue, determining just what should be considered an attack can get pretty tricky. Trying to hack other people's passwords, sure. Open spamming and verbal abuse in messages, most likely. Deliberate trolling, probably, but how easy is it to tell what the intent of a message was? Formalizing "good faith discussion" isn't easy. What about people sincerely posting nothing but "rationalist lolcat" macro pictures on the front page and other people sincerely upvoting them? Is a clueless commenter a 14-year-old who is willing to learn forum conventions and is a bit too eager to post in the meantime, or a 57-year-old who would like to engage you in a learned debate to show you the error of your ways of thought and then present you the obvious truth of the Space Tetrahedron Theory of Everything?
I'm not sure how what you say above is meant to influence what we recommend wrt possible changes to LW.
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).