I'm even more interested in system-level approaches to the problem. The voting systems of reddit and Hacker News and Slashdot are an improvement over the forums that came before, but more is possible. Are there any technologies that don't exist but could?
For example: an ebay-like system for rating someone's civility after you argue with them. (This might work better if ratings from well-rated people were weighted more.)
Or maybe an internet-wide troll-reporting system. There could exist a browser extension (maybe a part of the Reddit Enhancement Suite) that tags or hides comments from people who are frequently downvoted, or frequently rated poorly in the civility system.
Or a narrow AI that predicts your karma based on the words you use. If there are words that are often in downvoted or rated-uncivil comments (perhaps "lol", or "bullshit" especially if it's the first word in the comment, or "+1" especially if it's the entirety of the comment), it could warn you and check you want to continue.
Or if you're arguing in a domain-specific forum, like r/politics or r/economics, you're tagged with your score in a domain-relevant quiz (e.g. this for politically-relevant news: http://www.pewresearch.org/quiz/the-news-iq-quiz/).
Or a multi-variable voting system that asks for upvotes and downvotes for civility, apparent truth-seeking, agreement, and more.
Or much more broadly, what society-level interventions are possible? Lead exposure lowered IQ, and iodine-supplemented salt raised IQ, and IQ seems to cause (or at least be strongly correlated with) non-violence. Have we already made use of all the easy biological interventions like that?
Any other ideas? What systems will the most polite, truth-seeking internet forums of the 2020s use?