Point 1 is fairly straightforward. When most people talk about homosexuality as a sexual orientation they're talking experientially, not metaphysically. Unless you happen to be talking to a very committed gay philosopher who believes that his homosexuality forms the ontological matrix of his personhood, this argument commits a category error. The average gay, when he says “I'm homosexual,” means, “I experience predominate/exclusive sexual attraction for members of my own sex.” When he says “My homosexuality is innate,” he means, “I have had homosexual attractions for as long as I've had any attractions at all, and the tendency to have such attractions has probably been with me since birth.” The statement, “you are actually innately heterosexual” is meaningless in this context, because it has absolutely no referrent within his experience. It may be true, but it is true in a way that risks being alienating because it is not recognizable.
Truth should not be like that. Truth is effective when it is coupled with beauty in such a way that it resonates within the chambers of the heart. The heartstrings are plucked so that there is immediate recognition: Yes! That. Ita est. There is no need for a clever argument because it's obvious that the truth has been spoken, that the strings of my heart and the strings of the heart of the other are playing in tune. Christ's statements are always like that. He never argues. He just says things, and if your ears are open, and the heart is properly tuned, then it is obvious that what He's saying is True.
Which brings me to the second objection that I have with this argument. It states that the fundamental sexual orientation of the human person is heterosexual. I politely disagree. I think that the fundamental sexual orientation of the human person is Christological. All men are by nature designed to desire one flesh union with Christ, to be espoused to the Divine Bridegroom. All sexual attraction is merely a sign which points towards this. After the Resurrection of the Body there will be no human marriages – heterosexual marriage, for all of its dignity and loveliness, is a passing and ephemeral thing. The ethical dimension of heterosexuality therefore derives from its role as sign, from the fact that the spousal meaning of the human body points towards this ultimate meaning of human life.
For the majority of people, therefore, heterosexuality serves as a potentially ethical route for the expression of eros. It is not, however, essential. As John Paul II points out in Theology of the Body, eros has a multiplicity of meanings. It is in the Platonic definition that he sees a possible reconciliation between eros and ethos: “If we suppose that “eros” signifies the inner power that “attracts” man to the true, the good, and the beautiful, then we also see a road opening up within the sphere of this concept toward what Christ wanted to express in the Sermon on the Mount.” (TOB 47:5) This is a powerful idea, which suggests an alternative way forward for those who find the “straight” road impassible. Instead of trying to reorient homosexual desire towards heterosexual desire, it is possible to simply bypass heterosexuality and move directly towards Goodness, Beauty, Truth. This is the pathway which Socrates describes in the Symposium, a movement from the appreciation of the beauty of the beloved (in Socrates' account, a beautiful male youth), towards the appreciation of physical beauty in all of its forms, and from there an appreciation of the beauty of the mind, the beauty of institutions and laws, the beauty of the sciences and of knowledge, and finally “drawing towards and contemplating the vast sea of beauty, he will create many fair and noble thoughts and notions in boundless love of wisdom; until on that shore he grows and waxes strong, and at last the vision is revealed to him of a single science, which is the science of beauty everywhere,” and “when he comes towards the end will suddenly percieve a nature of wondrous beauty...beauty absolute, separate, simple, and everlasting, which without diminution and without increase, or any change, is imparted to the ever-growing and perishing beauties of all other things.”
Yes! That. Ita est.