This question already has an answer here:
Before down voting: If you down vote, leave a comment; the least you could do is prove that you care by leaving a comment of why you down voted. Down voting with no comment really only hurts the community more.. There hasn't been any good explination as to why no one is looking into this. Spam and "its a pain" just don't quite cut it. There are many ways to avoid spam, and laziness is no excuse.
The situation: This seems like a big conflict. New users are forced to gain more info on the sitautions through answers, which is something that is frowned upon. This seems good for commenting on answers, but requiring it for commenting on questions force new users to use an answer to gain more info from the OP. Now that I have enough rep to do reviews, it seems like a very common problem.
I understand that this leads to the possibility of spam, but there are ways to get around this. I think the combination of moderation of comments by people with under 50 rep and filtering comments to check for repetition, links, and any other things you feel would be good to look for (maybe relevance to tags/title; get creative). Of course it wouldnt be the easiest thing to do, but its definitely progress.