I think I like the idea. It's different from the "send private msg" thing, as it would presumably be done with one action instead of having to first vote and then in another action send the private message.

I don't have an opinion on whether it should be anonymous or not. For myself, I wouldn't care if people knew it was me being negative about their bone-headed ideas, but I suppose some people might want to hide who it is that's being stupid when they downvote such a clever person as me.