My simplified understanding is that the author is not advocating for punishing family members. Instead he is trying to discredit consequentialism, a position th

My simplified understanding is that the author is not advocating for punishing family members. Instead he is trying to discredit consequentialism, a position that an act is morally right based on the outcome. In that view retribution serves no utility since it doesn't maximize good and only causes suffering. The consequentialsit has to find a reason for punishment, and they say that it's a deterrence for future crime, which is a good outcome. But punishing families would also provide even more deterrence and the good from it would probably outweigh the bad of punishing innocent family members. But remember, a consequentialist should only care about the outcome so the act of punishing innocents isn't morally wrong in itself. The retributionist author on the other hand believes in the inherent morality of punishing criminals and immorality of punishing innocents.