I agree that sometimes the best comments are replies to otherwise "bad" comments, simply because the person replying is trying to correct/educate the bad commenter.

It's similar to Cunningham's Law – "the best way to get the right answer on the Internet is ... to post the wrong answer."

So by banishing all "bad" comments to the forever-pending state, perhaps this won't encourage the "better" commenters to come out of the woodwork to correct him/her.