Final answer:
Nathanson's argument against the death penalty questions the morality of a justice system that might occasionally execute an innocent person in the name of deterrence, stressing the importance of assessing the true impact of capital punishment on society.
Step-by-step explanation:
Nathanson's last argument against the death penalty, which can be seen as part of the 'second symbolic message' in support of his third main claim, revolves around the notion of morality in the context of justice systems that must sometimes decide between the lesser of two evils. He references anthropological reports of tribes where highly effective deterrence is achieved by enforcing a rule that if a member of tribe A kills someone from tribe B, a different member of tribe A would be killed. This creates a communal responsibility within the tribe to prevent killing. His argument highlights a paradox within capital punishment debates: is it morally acceptable to occasionally execute an innocent person if it leads to greater overall deterrence and less overall murder? His interrogation of capital punishment raises questions about morality, statistics on deterrence, and psychological impacts, ultimately disputing the morality of the system that endorses killing, sometimes even the innocent, as a form of justice.