It just shows the differences in views. Even something that is so obvious, logical, rational to you can be so ridiculous and downright stupid to others. But it will be healthy for discussion if they say why they downvote. It is like passing judgement without explaining your judgement. You don't win minds or opinions over from the downvoted person and the downvoter doesn't understand the other guy's point of view as well.
I downvote comments that don't add anything of value to the discussion. Why would I want to comment on something like that? By the very nature of commenting, I'm only doing the same thing the downvoted comment is doing: adding a post that adds nothing to the conversation.
Voting should have nothing to do with whether you agree with a comment or not. It should be indicative of the value of the comment to the discussion of the topic at hand.
