It is rational to be moral? Morality has evident advantages. A group of moral agents, able to co-operate by trusting one other, will do better than a group of amoralists. Co-operative civilized life is better for each than unconstrained conflict (the so-called state of nature). But this argument goes too fast. We can agree that morality generates social goods but rationality speaks to individuals. From the individual perspective the advantage of morality is problematic. Morality involves—at least—constraint; it requires that an agent sometimes act contrary to her own interests in favour of mutual advantage. Therefore moral behaviour generates a public good, available to all. However, rationality recommends free riding on public goods. The rational advice seems to be: let others practice moral constraint; remain amorally free to collect the benefits of others’ constraint. Of course, when all follow this advice, we end up in the state of nature, where no one is foolish enough to constrain herself.
Therefore from the point of view of rationality, morality is deeply problematic. This comes out in several ways. Our most developed social science, economics, is overwhelmingly cynical about moral motivation and pursues a programme of finding institutional replacements for morality. The received theory of rational choice, by defining rationality as unconstrained choice, makes morality irrational by definition. On the other side, most moral theorists have abandoned the attempt to provide a justification of morality in terms acceptable to a wider audience. The common methodological assumption that morality is an autonomous realm underscores the distance between morality and the sciences of rational choice.