I have noticed a few of my comments being down voted because people disagree with them lately. I feel that they qualified as substantial and weren't blatantly incorrect, but weren't what other people were looking for.
Downvoting a comment should be reserved for comments that we don't want other people to read. Things that are rude, blatantly false, or in general against the guidelines.
I don't think we should downvote things we disagree with, because to some users a downvote says, your comment isn't wanted here please take it somewhere else.
This isn't about points but instead the message you want to send to the author of the comment. If you do want to downvote someone because you disagree, could that instead be turned into a comment that might enlighten them and anyone else reading the thread?
Edit: I don't want to say that these downvotes were unfair, but more about users not following my subjective definition of the real purpose of a downvote which is to discourage conversation on that thread.