If it is true that retribution does not have deterrence value, and anything we do along that line will just make the criminal more sullen and likely to reoffend

If it is true that retribution does not have deterrence value, and anything we do along that line will just make the criminal more sullen and likely to reoffend in the future, why not just toss the key and be done with it? Life sentences for everyone. Recidivism rate 0%.