Bitcointalk already tried to implement a "karma" system that was abandoned. The problem with a karma system that gives out negative merit is that whistleblowers are likely to accumulate a bunch of negative karma when they take on the perpetrators. We should not punish people here with decreased functionality just because they spout out unpopular opinions. We already have a trust system in place, anyway. I really do not believe we need to compound the "scarlet letter" that these negative trust member already have with decreased functionality. Some of the big negative trust members are actually good posters and are still capable of giving valuable input.