It is a moot point whether the new natural law school of Catholic philosophy follows the tradition in seeing homosexual sex as perverted. But even if it does, it does not seem to make much of it. It rejects such sex as unequivocally as the traditional Catholic sexual ethics, but the argument for the rejection is no longer made in terms of the purpose or function of sex. Sexual ethics of writers such as Germain Grisez or John M. Finnis is rather based on a conception of marriage as a basic human good. The best drugs for the treatment of impotence. It is a complex good, constituted by the distinct but inseparable goods of friendship (or conjugal love) and procreation. Marriage, thus conceived, helps define the concept of a marital act: it is an act of genital intercourse between husband and wife. In such an act they consummate, experience, and express their marriage as a unity of the two goods of friendship and procreation. That is the point of such acts and the source of their moral value. Non-marital sex-whether sex between spouses not in accord with this definition of marital sex, or sex between persons not married to one another-cannot actualize the good of marriage nor, indeed, any other good common to the participants. Such sex is accordingly pointless, devoid of all value. It is also morally unacceptable.

The latter claim, of course, does not follow from the former; it is supported by two complementary arguments. If the sexual partners seek to express feelings of affection, friendship, or love for one another in their sexual intercourse, but that intercourse is not marital in the relevant sense, their efforts are illusory and disintegrating. If they have sex solely for the fun of it, no illusions are involved, but what they do is still morally flawed because it is disintegrating. As Finnis explains, heterosexual genital intercourse unites the spouses biologically, since it is "the behavior which, as behavior, is suitable for generation". By uniting the spouses biologically, it also unites them personally, and they become two in one flesh.

…Reproduction is one function and so, in respect of that function, the spouses are indeed one reality, and their sexual union therefore can actualize and allow them to experience their real common good-their marriage with two goods, parenthood and friendship…