An older but still amusing post from Marginal Revolution.
3. Freud was right and we are all repressed. The will is not unitary and the utility-maximizing part is not always in control.
4. There has been a market failure, but the Internet is remedying it. People are having more sex and this will only go up.
5. Sex stops being fun when you do it to close a gap between your marginal utilities. It requires spontaneity or some other quality inconsistent with the classical model of the consumer and the equation of marginal rates of substitution.