Chastity is the most unpopular of the Christian virtues. There is no getting away from it: the old Christian rule is, “Either marriage, with complete faithfulness to your partner, or else total abstinence.” Now this is so difficult and so contrary to our instincts, that obviously either Christianity is wrong or our sexual instinct, as it now is, has gone wrong. Of course, being a Christian, I think it is the instinct which has gone wrong,
But I have other reasons for thinking so:
- Biology: The biological purpose of sex is children, just as the biological purpose of eating is to repair the body. Now if we eat whenever we feel inclined and just as much as we want, it is quite true that most of us will eat too much: but not terrifically too much. One man may eat enough for two, but he does not eat enough for ten. The appetite goes a little beyond its biological purpose, but not enormously. But if a healthy young man indulged his sexual appetite whenever he felt inclined, and if each act produced a baby, then in ten years he might easily populate a small village. This appetite is in ludicrous and preposterous excess of its function.
- Striptease: Or take it another way. You can get a large audience together for a striptease act—that is, to watch a girl undress on the stage. Now suppose you came to a country where you could fill a theater by simply bringing a covered plate on to the stage and then slowly lifting the cover as to let everyone see, just before the lights went out, that it contained a mutton chop or a bit of bacon, would you not think that in that country something had gone wrong with the appetite for food? And would not anyone who had grown up in a different world think there was something equally queer about the state of the sex instinct among us?…
- Perversion: You find very few people who want to eat things that really are not food or to do other things with food instead of eating it. In other words, perversions of the food appetite are rare. But perversions of the sex instinct are numerous, hard to cure, and frightful….We have been told, till one is sick of hearing it, that sexual desire is in the same state as any of our other natural desires and that if only we abandon the old Victorian idea of hushing it up, everything in the garden will be lovely. It is not true. The moment you look at the facts, and away from the propaganda, you see that it is not.
—C.S. Lewis, The Joyful Christian, pp. 127-128 (Reformatted for readability)