Jeff McMahan proposes that states should permit active soldiers to engage in selective conscientious objection without significant punishment. McMahan argues that by forcing soldiers to fight in wars they believe unjust, states wrongfully compel soldiers to take grave moral risks. Since unjustifiably killing other human beings is the most serious moral wrong one can commit, the moral risk of doing so (individually or jointly with others) is grave indeed.

McMahan could strengthen his argument by attending to a different kind of moral risk inherent in military service. By participating in unjust wars, soldiers lose their own moral rights not to be intentionally killed or injured. Since these are the most important moral rights human beings posses, the risk of their loss is morally serious as well. If soldiers can reduce both kinds of moral risk through selective conscientious objection then the case for affording them this option is even stronger than McMahan suggests.

Of course, soldiers also take a moral risk by refusing to fight in a war that may prove just. However, McMahan offers several arguments to show that soldiers are more likely to selectively object to fighting in unjust wars than in just wars: that most wars are unjust; that governments are no better than well-informed soldiers at determining the justice of wars; that soldiers are inclined to believe wars are just (so if they believe otherwise they are probably right); and that evidence that a war is unjust generally is stronger when the war is in fact unjust than when it is in fact just. Unfortunately, these arguments depend on empirical and predictive claims that are at best overbroad.

Why not simply argue that it is morally wrong to compel a person to act against her conscience? 

Why not simply argue that it is presumptively morally wrong to compel a person to act against her conscience? Such compulsion infringes the moral integrity of the individual and corrupts her moral agency. Importantly, an argument from conscience goes through even if the conscientious objector is mistaken. For example, many states exempt pacifists from general conscription because forcing a pacifist to fight, even in a just war, would force her to violate her deepest moral convictions.

The subjectivity of conscience is also politically important because a state can respect a claim of conscience without conceding that its war may be unjust. It would be politically untenable for a state to say to its soldiers, “We have determined that this war is just, but we’re probably wrong, and anyway your guess is as good as ours.” The case for selective conscientious objection is stronger if it is both morally compelling and politically palatable.

McMahan also defines the scope of the right to selective conscientious objection very broadly. McMahan suggests that soldiers should be free to refuse to fight if their belief that a war is unjust is sincere and supported by plausible reasoning. But as McMahan knows all too well, even philosophers continue to disagree about the interpretation of just war theory—about the content and importance of traditional jus ad bellum criteria such as just cause, right intention, legitimate authority, last resort, reasonable chance of success, and proportionality. Moreover, careful application of these criteria to a particular conflict often requires expertise in intelligence analysis and international diplomacy as well as military strategy and operations.

McMahan’s rather permissive standard contrasts sharply with the parallel jus in bello standard, namely that soldiers have a right, indeed a duty, to refuse orders to commit particular acts that are manifestly unlawful—that are clearly unlawful under any plausible interpretation of the relevant law or facts. Perhaps soldiers should have a right to refuse to fight only if they believe a war is manifestly unjust, that is, clearly unjust even under the most permissive plausible interpretation of the jus ad bellum criteria and the most favorable plausible interpretation of the facts.

Put starkly, should a soldier have a legal right to refuse to fight if she plausibly believes a war is unjust, or should she have a legal duty to fight as long as her leaders plausibly believe the war is just? I am tentatively inclined toward the latter position. It seems that soldiers, unlike ordinary citizens, have at least some role-based duty to defer to the judgments of their civilian and military commanders when those judgments are not clearly erroneous. But I will leave the question for McMahan, and look forward to learning from his response.