Why? because you need to give some space to people to hit you on your ass then run fast. Hahaha!! That's pretty much what happens.
Seriously though, it doesn't matter. People who want to seriously discuss your answer, whether they agree or disagree, will comment on your answer. Other than that, we shouldn't take it too seriously because people may downvote you because they don't like you or that they REALLY disagree with what you're saying yet don't feel like saying anything. Others may give you an upvote just because they like you or for they REALLY like your answer yet not in the mood to add anything more or they don't think they have anything more to add. So, it can go both ways.
Everybody should do whatever he/she wants. It's a free world ;-)
I'm under the impression people upvote and downvote for different reasons. While some people may agree or disagree, many people downvote because they thought you weren't PC enough or didn't like what you said, even though they might not be able to say you're wrong.
I've noticed in the old version we could always the stats of votes, but now we have to vote in order to see them. I understand the concept of not being able to see them, but not sure if it doesn't defeat a little the purpose of being able to vote up and down.
I agree with you in that it would be better if people explained themselves when voting someone's opinions down. I don't think its so important that it needs to be regulated. I don't think about the voting much anymore because its all hidden now for some reason. Didn't really think much about it before either, haha.