A mandatory comment as to why someone -1'ed a post should be mandatory. Unless someone is intentionally being abusive/troll, then perhaps we should engage in the lesser popular viewpoints. Not doing so creates one hell of an echo chamber.

EDIT: currently at -1. You're only proving my point, buddy.

I'm not sure mandatory comments would solve the problem. We'd get plenty of the "I disagree." comments. Could those then be downvoted? Does downvoting those upvote the parent? Could I downvote both. Etc.

I don't know the current threshold but increasing it doesn't create an echo chamber. Look at any thread about gun control in the US and you will a lot downvoted comments on both sides and presumably a lot of highly upvoted comments on both sides as well. Not only that but you can only downvote comments until they reach a certain age. You can upvote them much longer (perhaps forever?). This creates a bias toward increasing votes which itself is a good reason to occasionally adjust the thresholds.