Actually, I think there's something to be said for downvoting. Not in the reddit "i disagree" sense, but in the slashdot/ >meta filter "comments downvoted/flagged past a certain point will be hidden/deleted" sense. It would obviously take a >lot of work to make that work within the media wiki software *and* the Wikimedia ethos, but it would probably save >tons of grief and derails if the worst of the worst comments were limited by crowdsourced review.
On the popular liberal/progressive website Daily Kos, the equivalent of downvoting, “hide rec”’ing, is meant to be used only for really offensive or out-of-line comments. Abusing that function, i.e., by constantly doing it to the same user or similar opinions reasonably expressed, can lead to sanctions against your account. Daniel Case