Scott Atran in the Huffington Post:
For despite the popular delusion that war is, or ought to be, primarily a matter of political strategy and pragmatic execution, it almost never is. Squaring the circle of war and politics, morality and material interests, is not just Obama's or America's quandary, it is a species-wide dilemma that results from wanting to believe with Aristotle that we humans are fundamentally rational beings, when in fact recent advances in psychology and neuroscience strongly indicate that Enlightenment philosopher David Hume was right to say that “Reason is, and ought only to be, the slave of the passions.”
Models of rational behavior predict many of society's patterns, such as favored strategies for maximizing profit or likelihood for criminal behavior in terms of “opportunity costs.” But seemingly irrational behaviors like war — in which the measurable costs often far outweigh the measurable benefits — have stumped thinkers for centuries. The prospect of crippling economic burdens and huge numbers of deaths doesn't necessarily sway people from their positions on whether going to war is the right or wrong choice. One possible explanation is that people are not weighing the pros and cons for advancing material interests at all, but rather using a moral logic of “sacred values” — convictions that trump all other considerations — that cannot be quantified.
As Darwin noted in The Descent of Man, and Sun Tzu millennia before in The Art of War, the brave person is the one who is often intensely moral, undismayed by danger and demonstrably willing to kill and die for his beliefs. In the competition between groups of genetic strangers, such as empires and nations or transnational movements and ideologies, the society with greater bravery will win, all things being equal. Consider the American revolutionaries who, defying the greatest empire of the age, pledged “our lives, our fortunes, our sacred honor” in the cause of “Liberty or Death,” where the desired outcome was highly doubtful.
How many lives should a leader be willing to sacrifice to remove a murderous dictator like Muammar Gaddafi or Saddam Hussein?