They can't. Any priest who violates the seal of confession is automatically excommunicated. Think of it like this.. in confession the priest acts in place of Jesus. We are confessing our sins to God. The priest is a conduit of God's mercy. You may not believe it, but we do.
Now, I support publicly flaying and impaling confirmed pederast priests. That said: Your last sentence is literally the exact opposite of the message of Jesus.