In re: Abu Ghraib, Mark Kleiman notes that moral and legal responsibilities need not sum to one across parties; thus, holding one person (say, a prison guard) responsible for the abuse of prisoners does not imply letting another person (say, Donald Rumsfeld) off the hook. A valid point, I think. But then Mark applies his principle to a substantially different issue, concluding that food corporations and their consumers are jointly responsible for the ill effects of obesity.
Mark and I have scuffled on this point before. As I said then, the argument for holding consumers responsible for their own actions while holding corporations blameless (assuming they have not withheld relevant information) does not rely on the notion of moral/legal responsibilities summing to one. Rather, it relies on the notion that the consumer is the only person in a position to decide whether the activity in question is harmful on net, since the benefits and costs are ultimately subjective.
Mark’s position rests on the implicit notion that moral/legal responsibility and physical causality are the same. They are not. Using a physical “but for” test, my grandparents are responsible for every sin that I commit. But for my grandparents’ decision to procreate, I would not have existed and thus would have committed no sins. So they are certainly “responsible” for my sins in a physical sense. Similarly, if I stop a woman on the street to ask for directions, and as she walks away she gets crushed by a falling piano, I am physically “responsible” for her death. But for my having asked directions, she would have continued walking and been safely beyond the piano’s future point of impact. Yet few people would hold my grandparents responsible for my sins, and no one (I hope) would hold me responsible for the death-by-piano. Clearly, moral/legal responsibility and physical causality are not the same thing.
From a legal or moral perspective, the issue not determining physical causality, but giving appropriate incentives. To conclude that it makes sense to hold someone legally or morally responsible for an act, and to punish him for it, you have to believe the act is in fact a bad one. I am comfortable making that judgment about the torture of prisoners at Abu Ghraib. Holding more than one person morally responsible for the torture will make it that much less likely that it will happen again.
But with respect to the eating of jelly doughnuts, I’m not comfortable concluding that the act is in fact bad. Jelly doughnuts have good and bad effects whose relative value can only be compared by the subjective preferences of an individual consumer. Holding Dunkin Donuts responsible for the ill effects would probably lead to fewer jelly doughnuts being eaten, but that’s not necessarily a good outcome.