The key justification President Obama evoked in going to war in Libya—and anywhere else around the globe where America’s survival and safety are not directly threatened—is that failure to act “would have been a betrayal of who we are.” The message is that America protects people who seek freedom and are subjected to violence by their own governments in the process.

Obama’s erstwhile presidential rival, Senator John McCain, countered that while this moral imperative may be laudable, “the reason why we wage wars is to achieve the results of the policy that we state.” And that policy, as the president himself proclaimed, is that “Qaddafi must go.”

Politicians and pundits across the ideological spectrum argue that the military mission remains murky, even contradictory, because as Admiral Mike Mullen, Chairman of the Joint Chiefs of Staff, put it: “the goals of this [military] campaign aren’t… about seeing [Qaddafi] go. It’s about eliminating his ability to kill his own people.”

So what is the sense of fighting to prevent Qaddafi from massacring his people if, as Adm. Mullen conceded, “certainly, potentially, one outcome” is that the dictator remain in power, probably to kill again?

Yet the apparent inconsistency between war as a moral imperative versus political policy runs way wider and deeper than the Libya conflict.

It goes to the heart of human nature and the character of society.

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 that we humans are fundamentally rational, when in fact recent advances in psychology and neuroscience strongly indicate that we are often ruled more by our 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.

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 Qaddafi or Saddam Hussein when it is not necessarily in the national interest?

Most of the theories and models that researchers use to study conflicts like the Libyan or Iraq wars assume that civilians and leaders make a rational calculation: If the total cost of the war is less than the cost of the alternatives, they will support war.

But together with Jeremy Ginges, a social psychologist at The New School for Social Research, I conducted studies of people confronted with violent situations in the US, Middle East and Africa which suggest that people consistently ignore quantifiable costs and benefits, relying instead on more esoteric beliefs.

In one study, we asked six hundred fifty-six Israeli settlers in the West Bank about the dismantlement of their homes as part of a peace agreement with Palestinians.

Some subjects were asked about their willingness to engage in nonviolent protests, whereas others were asked about violence. They were also asked to rate how effective they thought the action would be and how morally right the decision was.

If the settlers are making the decision rationally (in line with mainstream models) their willingness to engage in a particular form of protest should depend mostly on their estimation of its effectiveness.

But if sacred values come into play, that calculus should be clouded.

When it came to nonviolent options such as picketing and blocking streets, the rational behavior model predicted settlers' decisions.

Yet in deciding whether to engage in violence, the settlers defied the rational behavior models.

Rather than how effective they thought violence would be in saving their homes, the settlers' willingness to engage in violent protest depended only on how morally correct they considered that option to be.

We found similar patterns of “principled” resistance to peace settlements and support for violence, including suicide bombings, among Palestinian refugees who felt sacred values were at stake, such as recognizing their moral right of return to homes in Israel even if they expressed no material or practical interest in actually resettling.

This (along with other studies) suggests that most societies have "sacred rules" for which their people would fight and risk serious loss and even death rather than compromise.

Unlike other creatures, humans define the groups to which they belong in abstract terms. They make their greatest exertions, including killing and dying, not merely in order to preserve their own lives or those of the people they love, but for the sake of an idea—the conception they have formed of themselves. Whether the U.S. or the Libyan rebels stay the course or back down may well depend on how committed they are to a sense of “who we are” and the need to fight for it.