1.) The first difference is that there is a bona fide ethics of sexuality for Christians: Lust, fornication, impurity, same-sex desire, are all objects of moral condemnation and chastity, spousal love, marriage etc. are all sacramental, holy, and part of the divine plan.
2a.) The Christian has an ethics of sexual activity because sexual desire is a matter of rational and theological authority. The Christian stands in judgment of his desire.
2b.) The Christian approaches sexuality through a series of paracletic exhortations received in faith from those speaking at the highest level of mystical prayer, taken to be in a position to know what makes man happy. Whoever looks at a woman with lust has already committed adultery with her in his heart. For freedom God has set you free… let not your members serve impurity. Do you not know that your body is a temple of the Holy Spirit who dwells in you? Glorify God with your body. Walk by the Spirit, and you will not gratify the desires of the flesh. For the flesh desires what is contrary to the Spirit, and the Spirit what is contrary to the flesh. The acts of the flesh are obvious: sexual immorality, impurity and debauchery… I warn you, as I did before, that those who live like this will not inherit the kingdom of God.
3.) The absence of contemporary sexual ethics is precisely absence of authority over desire. Sexual desire is taken as conferring identity – hetero, homo, pan, whatever – that must be respected, celebrated, protected, indulged. We can have no ethics because we can have no judgment of desire but only acceptance of it. Those who might find some “perversion” to be “icky” still see their own desires as conferring on them an “identity” that God gave them making them who they are. This is lust.
4a.) For the Christian this is the fundamental error of the contemporary sexual un-ethics is that desire is not to be judged by a mystic in a better position than ourselves to know what makes one happy and what God intends. If it is only a question of voluntary action, of what we want to do or what feels natural to us then there is no ethics, and this is the fundamental stance that contemporary persons are trained to take toward sexual activity. If the “right amount to drink on a weekend” is whatever one feels it should be, there can be no ethics of drinking, only the celebration of our identity as teetotalers, Alcoholics, spring-breakers, Baptists, etc. In the same way, whether we take ourselves as “heterosexual” or “homosexual” or parasexual, if the desire is taken as conferring identity then reason and theology must give way. I am understood not as a rational animal but as an animal moved by passions and desire. This too is lust.
4b.) The dividing thesis: as passions a matter of rational and theological authority?
5.) We contemporary persons have no sexual ethics because sexuality, we think, is what we are to give way to or give in to. What else could acceptance and celebration mean? The desires we find in ourselves are seen as “God” or “how God made me”, i.e. it is (a) the titanic force that cannot be restrained, and (b) is no one’s business but our own anyway. The first is presented as romantic and mysterious but is in fact degrading and debasing; the second is patently non-empirical and childish. Our sexual desires create family-strength bonds and so tie us to others and tie those others to those to whom we are already so tied. Our lovers and spouses have a way of showing up on holidays, vacations, family cabins, family pictures, etc. Sexual activity cannot be ever just our own business.
6.) The desire for family is judged by whether the action extends family, and the human family extends not by our being overcome by titanic forces that “God” somehow “places in us” but by coupling, inseminating, impregnating, bearing and raising. Desires outside of this sphere are simply mistaken.
7.) Lust is thus fundamentally a rejection of authority and faith, and so a handing over of what are, in fact, our higher powers to our lower ones. There is a demonic inversion of the true God in excelsis who reveals and stands in authority over nature, and these natural powers are themselves renamed and usurp the name of “God.”