The article cited below gives a number of ways NOT to respond to online defamation, but I want to zero in the focus on his first point. Never ask a blogger, or commenter for that fact, to remove a post. For one, if you comment on their posting–this will only give them more fuel for the fire, and it will increase the visibility of their posting. Secondly, it is highly unlikely that the blogger will remove the posting anyway–he will, more than likely, bristle about freedom of speech.
http://www.davidrisley.com/2009/02/26/negative-publicity/