OK, I know this has been discussed before many, many times but I'd like to make a new suggestion.
Problem: drive-by downvoting - people downvote without explaining why. And when you downvote, legitimately, you lose rep, as does the questioner / answerer. This strikes me as being a lose / lose situation.
Previous solutions: e.g. here and here have required forcing comments.
Solution: How about this instead: keep the current system (downvoter loses rep) unless the downvoter adds a comment in which case no rep is lost. I think this is win/win. The downvoter can choose to enter comments but is encouraged to do so, which increases the feedback to the original questioner / answerer.