Maybe classification like this would be helpful: "up" (=well written/insightful/continues the discussion) xor "down" (=spam/rude/trolling/prevents discussion), "agree" xor "disagree", or "problematic" (=bad grammar/bad-language usage/logical flaws/prospect of improvement). Comments would still be mainly sorted by up/down counts, partly by the count of reported problems. The agreement-percentage will be displayed for everyone and the problems will be displayed only to the commenter so that the comment can be improved accordingly.