If you want to nuke trolling, use the Metafilter strategy: new accounts have to pay $5 (once). Troll too much, lose your account and pay $5 for a new one. Hurts a lot more than downvotes.
It's a good idea. Some variations, like associating accounts with mobile phone numbers, may slow good growth less. Maybe it would help to have multiple options to signal being a legitimate new user.
Casual users don't contribute to Less Wrong's mission: we need more FAI philanthropist/activists.
I would like to see more x-risk philanthropists/activists, but I don't want to make that a requirement for LW users. It would be good to have more users who want to be stronger because they have something to protect, rather than thinking rationality is shiny.
associating accounts with mobile phone numbers
I don't have a phone, and if I did I would refuse to give it out in case someone did something horrible like call me. I'm not the only phone-hater around; we overlap with phone-hater demographics a fair amount.
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).