It would be nice if downvoters had to add a compulsory comment, though I suspect many users would create a special login they use just for downvoting. HN is a lot better than other sites though, such as Reddit, where some subreddit moderators often delete comments after you've replied to them, leaving your own reply as an invisible orphan.
> It would be nice if downvoters had to add a compulsory comment.
It would directly defeat the purpose of downvoting in terms of reducing the prominence and visibility of non-productive comments if large # of downvotes mandated that a comment become the branching point of a heavy subthread.
