NOTE Why Most (but not all) Churches Hate Sex Guido ORTONA Dep. POLIS, Università del Piemonte Orientale, Via Cavour 84, Alessandria 15100, Italy. E- mail: guido.ortona@sp.unipmn.it Abstract Churches have the power to decide what is a sin, and are empowered to pardon sinners. This is sufficient to explain why many common sexual practices, like the use of prostitution, are serious sins. Keywords: Sin, Economics of Sin, Church, Economics of Church. 1. Introduction In this paper I will suggest a theoretical reason why a Church (as such, i.e. irrespectively of its doctrine) may be expected to be sexophobic in due, and common, circumstances. The argument will be discussed through a very simple model. The first prevision, as we will see, is the very sexophobia of the Church(es); others will qualify this result. To keep the discussion as simple as possible, I will consider only a typical case, that of classic prostitution, where (a) a man pays a woman to engage in sexual intercourse with him and (b) the woman is motivated only by monetary reward. However, the results may be easily generalized to a cohort of other sexual behaviors, and possibly to a cohort of completely different settings, as will be suggested at the end of appendix 1. First, the assumptions; being such, I will not provide any argument to prove them, except some footnote observations. I only claim that their validity seems to me empirically proved beyond any reasonable doubt. They are three, in addition to the usual ones in economics. a) If heterosexual intercourse has no cost, there is an excess demand from the male side. 1) Evol. Inst. Econ. Rev. 3(2): 261–273 (2007) JEL: Z12. 1) I share the view that this feature is biological. Two arguments support this conjecture. First, excess demand is a constant in all human societies so far discovered, bar unusual non-equilibrium settings (such as a society lacking men due to a war), as well as among all other mammals (at least). Second, and more cogently, there are sound optimization reasons for it (see f.i. Dawkins, 1976, ch. 9; Trivers, 1972). However, this is not crucial for our story, provided that the presence of excess male demand is accepted.