“The great classical philosophers would have regarded it as an absurdity, despite their partial tolerance of homosexual love.”
The central insight of classical Greek philosophy is that the order of the city is the order of the soul writ large. If there is disorder in the city, it is because of disorder in the souls of its citizens. This is why virtue in the lives of the citizens is necessary for a well-ordered polis. This notion is reflected in the Athenian’s statement concerning the political benefits of the virtue of chastity.
This is why Aristotle forbids adultery, wants to make it disgraceful in all circumstances, not only because it subverts virtue, but because it attacks the political foundations of society. Adultery becomes a political problem because it violates chastity, which is indispensable to a rightly ordered polis. There is no comparable condemnation of adultery in homosexual marriage in Aristotle because such an institution would have been inconceivable to him, as it has been throughout history until recent times. That is because it is a self-contradiction. Marriage cannot be based on an act which is in itself a violation of chastity, because something cannot be its opposite. A homosexual household would not make sense to Aristotle since it could not contain parents and all the generational relations that spring from them, which makes the polis possible. What did not make sense then still does not make sense now, and for the same reasons.
What is and has been the age old teaching of the Church on the matter of chastity and homosexuality?
2357 Homosexuality refers to relations between men or between women who experience an exclusive or predominant sexual attraction toward persons of the same sex. It has taken a great variety of forms through the centuries and in different cultures. Its psychological genesis remains largely unexplained. Basing itself on Sacred Scripture, which presents homosexual acts as acts of grave depravity,141 tradition has always declared that "homosexual acts are intrinsically disordered."142 They are contrary to the natural law. They close the sexual act to the gift of life. They do not proceed from a genuine affective and sexual complementarity. Under no circumstances can they be approved.
2358 The number of men and women who have deep-seated homosexual tendencies is not negligible. This inclination, which is objectively disordered, constitutes for most of them a trial. They must be accepted with respect, compassion, and sensitivity. Every sign of unjust discrimination in their regard should be avoided. These persons are called to fulfill God's will in their lives and, if they are Christians, to unite to the sacrifice of the Lord's Cross the difficulties they may encounter from their condition.
2359 Homosexual persons are called to chastity. By the virtues of self-mastery that teach them inner freedom, at times by the support of disinterested friendship, by prayer and sacramental grace, they can and should gradually and resolutely approach Christian perfection.