Good point.

One way to look at it is this: the priest hears the confession, not as his own person, but acting in the person of Christ. The confession is to God, mediated by the priest. The priest is not the privileged recipient, and hence has no right to divulge anything whatsoever said between the penitent and God through him.

Now a horrid man's plans are already known by God, but God does not divulge them, does He? He could... He could reveal the plans of a child molester, but He does not. If He does, that is His right. But it is God's right, not the priest's here.