I think the solution would be to just make the down-vote do nothing but increment the visible counter, and also make it so that users that can't comment if they already voted. This allows people to simply signal their disapproval without fighting repetitive flamewars in the comments or suppressing content they don't like.

Or maybe if you're running a forum where you want to promote controversial content and hide boring content, just make the downvote act identical to the upvote, so users are incentivized to downvote and argue if they think it is argue-worthy and just ignore if they think it is too boring to discuss.