The model of human action as resting on rational choices between alternative opportunities for maximizing our utility has been borrowed from liberal economics by social scientists keen to refute the conventional explanation of secularization. This chapter considers whether we can treat religion as a commodity that people buy more or less of according to individual rational choice. It argues that religion differs from soap powder both extrinsically (because we cannot readily compare its costs or benefits) and in terms of its social roots: in most societies switching religion threatens social bonds far more than does changing car brands. Finally, it advances an important general principle: that we should be very reluctant to impute to other people motives that we would not impute to ourselves.