Finally, some hold that the death penalty is incompatible with the teaching of Jesus on forgiveness. This argument is complex at best, since the quoted sayings of Jesus have reference to forgiveness on the part of individual persons who have suffered injury. It is indeed praiseworthy for victims of crime to forgive their debtors, but such personal pardon does not absolve offenders from their obligations in justice. John Paul II points out that “reparation for evil and scandal, compensation for injury, and satisfaction for insult are conditions for forgiveness.”
The relationship of the State to the criminal is not the same as that of a victim to an assailant. Governors and judges are responsible for maintaining a just public order. Their primary obligation is toward justice, but under certain conditions they may exercise clemency. In a careful discussion of this matter Pius XII concluded that the State ought not to issue pardons except when it is morally certain that the ends of punishment have been achieved. Under these conditions, requirements of public policy may warrant a partial or full remission of punishment. If clemency were granted to all convicts, the nation’s prisons would be instantly emptied, but society would not be well served.
Avery Cardinal Dulles, “Catholicism & Capital Punishment” (2001)