The paper presents a model of ‘rational irrationality’ to explain why political and religious beliefs are marked not only by low information (as the notion of rational ignorance highlights), but also by systematic bias and high certainty. Being irrational – i.e., deviating from rational expectations – is modeled as normal good. The reason that irrationality in politics and religion is so pronounced is that the private repercussions of error are virtually nonexistant. The consumption of irrationality can be efficient, but it will usually not be when the private and the social cost of irrationality differ – for example, in elections.