I probably agree that if downvotes were only for off-topic/trolling/unhelpful comments the situation would be better, but I don't think we're there; I am fairly confident that downvoting for disagreement is common and officially okay.
>>almost+97
on a technical level, being able to see downvotes and upvotes separately would actually be interesting, as it does carry a signal, but it probably doesn't happen often enough to be worth the effort to implement.