People want both (as separate values) safety from crime and retribution for crime. In this thought experiment, zero punishment is stipulated to maximize safety from crime, but it simultaneously minimizes retribution. If marginal [value of] retribution at zero punishment is lower, then zero punishment is optimal, otherwise a non-zero amount of punishment is better overall. Alternatively, if the only available forms of punishment are such that the aspect of (undesirable) hurting of criminals outweighs the aspect of (desirable) retribution for the crime, then zero punishment is automatically optimal in this thought experiment.
People want both (as separate values) safety from crime and retribution for crime. In this thought experiment, zero punishment is stipulated to maximize safety from crime, but it simultaneously minimizes retribution. If marginal [value of] retribution at zero punishment is lower, then zero punishment is optimal, otherwise a non-zero amount of punishment is better overall. Alternatively, if the only available forms of punishment are such that the aspect of (undesirable) hurting of criminals outweighs the aspect of (desirable) retribution for the crime, then zero punishment is automatically optimal in this thought experiment.