Down-voting is awkward. Some feel it should be reserved for extraordinary circumstances, others that it's essential for every day curation of the site. Frequently, the person being downvoted does not know what they did wrong. But if all downvoters were to explain their reasons, far too much attention and page space would be spent on poor comments.
Proposal: The downvote arrow takes you to a "confirm" page with a "reason" text box. If you want to downvote you are encouraged (required?) to enter a reason before confirming your vote. This page also shows otherwise hidden comments by other people explaining their downvote.
Advantage: Allows downvoters to explain to the commenter why their comment is being downvoted without cluttering up the main discussion page. Ideally produces a better and more functional community.