Dr. Casey, thanks for your reply. I agree that morality has to be based on human flourishing and that what counts as human flourishing depends on human nature and, in particular, on the biological functions of our natural faculties (just not in the way the perverted-faculty argument assumes). And I also agree that we are sometimes justified in holding moral beliefs based on our moral intuitions, just as we are sometimes justified in holding aesthetic beliefs based on our sense of beauty. However, the more controversial a (moral or aesthetic) opinion is, the more it is in need of argumentative justification.
Thank you for pointing me to the article by Charles Capps. I like his arguments against classical and “new” natural-law theories and his proof that the sexual drive is naturally directed towards the conjugal act (i.e., a sexual act which occurs within a loving relationship and tends to result in children who are then lovingly raised by both parents). But his own defense of traditional sexual morality is unconvincing; if I am not mistaken, it goes roughly as follows:
1. Altruism (self-giving love) is the sum and essence of morality; i.e., we should always behave as altruistically as possible.
2. The conjugal act is more altruistic than other kinds of sexual acts.
3. Therefore, the conjugal act is the only permissible kind of sexual act.
Premise 2 is plausible (given Capps’s definition of “conjugal act”), but you don’t need to be an Objectivist to see that premise 1 is highly problematic (and inadequately defended by Capps). Self-sacrificing love is just one of many human goods; consequently, there can be an excess of it (such as when someone sacrifices his life to spare a stranger a small inconvenience).
But even if premise 1 were true, the argument would be invalid (and here we return to logic). The premises merely show that the conjugal act is to be preferred over other kinds of sexual acts when both options are available.