+1. The moral basis for much of our societal rules and behaviors is unsound if free will is incompatible with biology. We in the US do so many things based on Puritan moral views that are so very harmful and counterproductive to our goals, based on an incorrect understanding of how the world works.
The existence of punishment changes the inputs to the system and, thus, changes the outputs of the system. The system in this case being the mind and it's output being behavior.
Right which is why I specifically said retributive justice. Other penal forms may still be morally justified for the sake of the “system” as it were.
But the very existence of ethics is in danger in absence of free will. Existence : as in, whom do you blame for hanging the terrorist ? The lawyers, judges, jury, witnesses did not have free well : so it was inevitable that the terrorist be hanged.