I'm writing this answer after the change in rules to downvoting. That is downvoting questions no longer costs reputation points.
From everything I've read on stackoverflowStack Overflow, comments, edits, and good answers are encouraged. I've taken that philosophy to heart. I believe that downvoting is not constructive if there is no comment to accompany it. And, a comment will usually encourage some questioners to edit their original question, at least that's how it works with me.