Suppose I get my clothes wet and dirty pulling a couple of children from a giant puddle. I'm part of a group on a picnic involving several families, the two children have been playing in the puddle, they've fallen over and are crying. Have I behaved irrationally by muddying my clothes in the interests of others? Suppose you delay a purchase you've long wanted to make, in order to put in a large donation to UNICEF. Is your decision, because altruistic, irrational? I wouldn't have thought so. But that seems to be the concept of rationality and its opposite that's in play here:
[T]here is robust evidence that unreasonable anger against those who harm the common good is deeply embedded in human DNA - and has probably played a salutary role in our economic, political and social history.
A wide body of experiments have recently put such anger in a new light: Seeking to punish those who harm the common good, especially when the punishment involves a high cost to ourselves, is really a form of altruism. As with giving to charity, "altruistic punishment" elevates emotional goals over purely rational - and selfish - goals. You see altruistic punishment on display anytime a person puts his life at risk to apprehend a criminal or spends her own time and money to bring wrongdoing to light.
Altruistic punishment has been found in every human society scientists have studied; it has even been found in other species.
If I act at a cost to myself but in order to help someone else, including a wider social group to which I belong, there need be no irrationality. Some of my goals may be other-regarding ones, why not? And provided that I pursue effective means to achieve those goals I'm acting perfectly rationally. It might be said, I suppose, that there are no truly other-regarding goals; we want the satisfaction - a personal reward - that we get from acting unselfishly. I don't accept this, but even if it were true, it wouldn't validate the concept of rationality implicit in the column from which I've quoted. Rather the opposite.