You bring up a good point. I wonder if Dreher spoke to the priest before he published the details of the priest's past.
Seriously, correct me if I'm wrong, but isn't detraction the sin of exposure of someone else's serious sins "without sufficient cause"?
Sex abusers have an extremely high rate of recidivism, such that U.S. law requires the registration of those convicted of this crime even after they have served their prison sentence; and clinicians have observed for 40 years that pedophilia is virtually incurable. (Google "sex abuse incurable" to get a range of opinions on this: a range, by the way, but none of them optimistic.)
This being the case, even if this sin has been confessed and forgiven, and the abuser has done penance, he should be permanently prevented from having any contact with children and youth. If the Bishop put this priest in a parish, the faithful who know about the man's background have not just a right, but a duty, to make it known.
Protecting parishioners and their families from a man with a history of sex abuse is "sufficient cause" to blow the whistle.