negative karma that doesn't discourage the poster from making further similar comments is almost pointless.
Comments don't have to be "bad" to be worth hiding -- they can just be "not very good" or "not very good anymore" . The fastest way to improve a document is to remove the least good parts, even if those parts aren't "bad". Many comments are necessary at the time, but fluffy afterwards ("By foo do you mean bar?", "No, I meant baz, and have edited my original post to make that clear", "OK, then I withdraw my objection"). If two people independently offer the same exact brilliant insight, we'd should still hide one of them. There are no shortage of times I'd like to hide a comment without discouraging or punishing the author.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.