What's abusive about it? You'd rather he lose more karma from a mistake that he's already learned from?

It appears that the original comment was made with the intent of immediately retracting it. "Learning from a mistake" is not a reasonable description of that behavior. But Larks' solution is not a good idea because two wrongs don't make a right (in this circumstance).

That said, I agree with you that retraction of a comment that one is surprised is heavily down-voted or otherwise learns later is wrong is a very reasonable reaction.