At the the inscrutable Becker-Posner blog (run by two professors from my alma mater) Judge Richard Posner ponders The Sexual Revolution:
Let us consider first why sexual morality has changed so much over the past half century. If one takes an economic approach to the question, then since the benefits of sex in the sense of the pleasure or relief of tension that it yields have deep biological roots, it is probably to the cost side that we should look for an answer. The costs of engaging in sexual activity have fallen dramatically over the last half century (AIDS notwithstanding), for many reasons.
Read the rest if you like. You’ll learn why the service economy has destroyed the institution of marriage, and that in turn has lead to rampant homosexuality.
Dr. Becker responds with his own Comments on the Sexual Revolution:
So it is possible to understand the basis of the sexual revolution using an “economic” approach, but the approach must recognize that norms and habits are also important. These norms and habits usually adjust eventually to new forms of behavior, and the new norms greatly accelerate this behavior after they do adjust.
I disagree with Posner that sex will become, either morally or in other ways, just another consumer activity, like eating. Sexual intercourse is a very intimate relation between two people that grew as humans evolved during the past 50,000 years when they apparently began to separate into families. This relation carries a lot of emotional attachment and baggage that will not vanish simply because contraceptives are effective and birth rates are low.
I especially like the way Becker shows how evolution can be used to argue for social norms.