If I were to do this analysis, there are a few dimensions I would look at first to see how much variance they account for:

• ratio of words devoted to negation, vs. words devoted to proposing an alternative idea or to asking for clarification

• nonresponsiveness... that is, where comment C1 = X, and C2 = "-X, because Y1..Y3", and C3 = X with no significant addressing of Y1..Y3. (This is a little tricky, though because in general I expect the absolute value of karma scores to decrease the more nested they are.)

• the combination of stridency and incoherence. (Either in isolation I wouldn't expect to account for much negative karma.)