There is no perfect system. Some under threat of the death penalty will kill their victims; however, some kill their victims even now at the threat of being beaten to death in prison.
It would send a strong message to have a few well-publicized executions if the victim was severely harmed; especially if the rapist forced them to abort a child resulting from the rape(s). That would indeed be an eye for an eye.
Of course child molestation is exponentially more serious than pickpocketing but the principle's the same. Kill the kid and she/he can't tesitfy against you.