I agree about the seriousness of the problem, but disagree about the solution. Giving anyone the power to delete any comments from their articles could be abused easily.

How about a compromise solution: a special "extra vote down" button, available only for the article author, giving -5 karma to a comment? That is enough to make a new comment collapsed, but can be reversed by enough votes from the readers. The probability of readers upvoting a trolling comment en masse is in my opinion not greater than the probability of an author to downvote a comment for wrong reasons. (Also, the number -5 can be adjusted later, if the value seems wrong.)