I found an interesting article about the psychology of war ("why war is never rational"). It basically says that sometimes we humans can be perfectly rational and balance costs and benefits while at other times we seem to lose all rationality. The latter happens when we think that a moral issue is at stake.
Of course at a certain level science is telling here once again what we already know. But on the other hand it is good to have it explicit as through the course of history populist leaders have been very good in raising our moral indignation about things that previously didn't bother us. It is also good to realize that a seemingly innocent change in a situation can change people's view from the rational to the moral side. The article provides some nice examples both from science and the real world.