Cost and Benefit

Yglesias on the Stiglitz study:

They make a solid case for a $700 billion to $1,000 billion direct cost plus some fairly uncertain macro consequences. Of course, on the one hand this seems like an odd way to think about a question of war and peace.

But on the other hand, the very high direct costs are something that has to be kept in mind when considering the humanitarian benefits of the war. This is a staggerly large sum of money that could have been directed at much more useful causes if people really felt that a $1 trillion humanitarian initiative was something they wanted to get behind.

Why does a cost-benefit analysis seem like an odd way to think about a question of war and peace? Every decision about whether or not to engage in a war (either offensive or defensive, really, but particularly in the case of wars of intervention), is about purchasing some probability of some good at some probability of some expense. The good may be peace, security, democracy, whatever, and the expense will include blood and treasure. Evaluating whether the expenditure of blood and treasure is worth the achievement of the good in question seems to me to be a perfectly natural, and appropriate way of deciding to engage in a war.

I’m not trying to pick on Matt, because his is not the first implication I’ve seen that the decision on whether to go to war shouldn’t follow a rational decision-making calculus (whether it actually is historically descriptive or no), and he comes to the correct answer. Nevertheless, I’m curious why people find this formulation even mildly troubling.