From Science:
How many lives would you be willing to sacrifice to remove a murderous dictator like Saddam Hussein? Most of the models that researchers use to study conflicts like the Iraq war 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 according to a new study, those models are wrong. Surveys of people in the Israeli-Palestinian conflict and other violent situations suggest that participants consistently ignored quantifiable costs and benefits, relying instead on “sacred values.” The finding could lead to better predictions of when conflicts will escalate to violence.
Models of rational behavior predict many of society's patterns, such as the prevalence of tax evasion and union strikes. But seemingly irrational behaviors like war—in which the measurable costs often far outweigh the measurable benefits—have stumped researchers going back to Charles Darwin. 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 at all, but rather using a moral logic of “sacred values”—convictions that trump all other considerations—that cannot be quantified.
More here.