Chris Purcell at Meatball Wiki addresses the same question as Theresa's.

<< You might need a trust metric to stop relatively untrustworthy users, who have simply kept well-behaved until then, retroactively reverting all a respectable user's posts and thus zeroing his trust. >>

http://www.usemod.com/cgi-bin/mb.pl?action=browse&diff=1&id=TrollDet... onFormula

Ed Poor