Mutual Advantage vs. the Draft

— In his reply [scroll down] to Judge Posner's defense of an all voluntary military, Bill Galston writes:
Let's begin with a conception of society as a system of cooperation for mutual advantage. A society is legitimate when the criterion of mutual advantage is broadly satisfied (versus, say, a situation in which the government or some group systematically coerces some for the benefit of others). Each citizen then has a duty to do his or her fair share to sustain the social arrangements from which all benefit, and society is justified in using its coercive power when necessary to ensure the performance of this duty. As John Stuart Mill, whom Posner wrongly drafts into the anti-conscription army, states in On Liberty, the state may legitimately require each citizen to bear “his share … of the labours and sacrifices incurred for defending the society or its members from injury and molestation.”
A counterargument urged by the late Robert Nozick is that we typically don't consent to the social benefits we receive and that the involuntary receipt of benefits does not trigger a duty to contribute. Mill anticipated, and rejected, that thesis, insisting that the duty to contribute does not rest on a social contract or a voluntarist account of social membership. Besides, the argument Socrates imputes to the Laws in the Crito is compelling: If a society isn't a prison, if as an adult you remain when you have the choice to leave, then you have in fact accepted the benefits along with whatever burdens the principle of social reciprocity may impose.
OK. I like to begin with the idea of society as a cooperative venture for mutual advantage. But Galston's argument moves way too fast. (It is a letter to the editor, so I admit that it's not fair to expect a tight argument.) I'm sure part of my problem stems from the fact that I have a stricter conception of what it means for the “criterion of mutual advantage” to be satisfied. Suppose Galston's right, and citizen's have a duty to do their share to sustain the system. Well, it's a non-sequitur to move directly from a duty of a citizen to do her fair share to a permission for some other citizens, as agents of a government, to use coercive means to ensure the execution of the duty. Granting some a right to employ coercion, while denying that right to others, creates a form of inequality that is morally troubling on its face. The suggestion that this sort of inequality in coercive power be institutionalized requires a special justification in terms of it's effect on mutual advantage. But suppose we find some justification. It remains open what a “fair share” requires. If an all volunteer military is MORE effective than a conscripted military, and requires LESS sacrifice and burden then conscription, then it seems obvious to me that, from the perspective of cooperation to mutual advantage, a volunteer system is better justified. If sacrifice and burden are unnecessary–if you don't need to interfere with people's pursuit of their personal projects over and above the level of taxation required to provide the good–then a system that demands it will straightforwardly fail the mutual advantage test.
Furthermore, the positions from Nozick and Mill that Galston plays against each other are perfectly compatible. Nozick is right that positive externalities don't necessarily trigger a duty to contribute. I have no obligation to throw quarters at attractive women walking past on the sidewalk. (Econo-geek code: “Got a quarter?” = “She's hot.”) Nor do I have a duty to contribute to the R&D costs of a company that develops a vaccine, the side effect of which is that a disease dies out, and I therefore never get exposed to it, even though I was never vaccinated, and never gave a red cent to PharmaCorp. The beauty of a system of cooperation for mutual advantage is that the private pursuit of private ends creates positive spillovers that benefit us all, and the private actors creating the benefits are generally happy to internalize the costs because a disproportionate amount of the benefits accrue to them. We want a system where it is possible for everybody to constantly free ride, but where nobody minds.
And Mill is right that the duty to contribute does not require explicit consent. But whether explicit consent is required to justify a system where some are granted powers to coerce others into contributing according to duty is an entirely different question. (Again, P has a duty to A does not even BEGIN to entail that S is permitted to coerce P to do A. It may be that S always has a duty to refrain from coercing P, no matter what other duties P has.) In any case, we're all already meeting our duty to contribute insofar as we're paying the taxes that pay the salaries of the people who have volunteered to internalize the risks of serving in the military. The logic of Galston's argument, even if we grant him premises about the justification of coercion in the service of mutual advantage, only gets him as far as the current system. He doesn't HAVE an argument for conscription. If he thinks we have a duty to serve in the military even though the voluntary system is most effective and places lower burdens on citizens at large, then he has abandoned the principle of mutual advantage as the basis of political obligation.