There are three main counterarguments against my overarching thesis in Parts 1-3; namely, that adult-committed incest and polyamory are better analogies to homosexuality and transgenderism than are race and gender. None of them are convincing, in my view.
First, supporters of homosexual unions will sometimes argue that there are no significant sexual differences between men and women, often appealing to a strict social-constructionist philosophy. The problem is that most people don't live in accordance with such a perspective, including most persons who identity as "gay" or "lesbian." Why is it the case, for example, that the vast majority of homosexual men would not (or claim not to) be fully satisfied with a sexual relationship involving a woman, even a particularly gender-nonconforming, masculinized woman? Why do they regard themselves as a "category 6" on the Kinsey spectrum? Could it be that they tacitly recognize that there is an essential maleness to men that not even a gender-nonconforming woman can successfully reproduce?
If there were nothing essential or significant to male-female differences then we should expect nearly the whole American population to be bisexual rather than "unisexual." Yet, as it is, over 98% of the population (possibly over 99%) is strongly disposed to sex only with members of one sex, whether the other sex (heterosexuals) or the same sex (homosexual). There must then be a fundamental difference between maleness and femaleness that, in turn, constitutes a radical difference between heterosexuality and homosexuality. The former is sexual arousal for the sex that one is not but which complements one's own sexuality. The latter is sexual arousal for what one already is as a sexual being and does not truly complement one's sexuality. They are not simply two different sexual orientations that are otherwise of equal developmental naturalness and soundness. One is intrinsically disordered and it's not heterosexuality.
The second potential argument against my thesis is that congenital causation factors for some homosexual development (which factors, in any case, are neither total nor deterministic) make homosexual desire and behavior "natural." This argument misunderstands the elementary point that persons can have innate or involuntary desires for behaviors that remain unnatural on other grounds. Pedophiles, for example, don't "choose" to be pedophiles in the normal meaning of the term "choice." Even so, the absence of choice does not make sexual intercourse with children "natural" in the truest sense of the word because children are structurally or formally incompatible for sexual intercourse with an adult. My point here is not to claim that in all respects homosexual practice is as bad as pedophilia but rather to make the singular point that the innateness of a sexual orientation does not make the behavior arising from the desire "natural."
Moreover, we all know that innate urges are unreliable guides for moral behavior. An argument for homosexuality based on biological causation is not an effective moral argument because, as even admitted by two scientists who have studied extensively biological causation factors for homosexuality and who support homosexual causes: "No clear conclusions about the morality of a behavior can be made from the mere fact of biological causation, because all behavior is biologically caused" (so J. Michael Bailey of Northwestern University and Brian Mustanski of Indiana University).
The third argument is that homosexual practice cannot be compared to incest or polyamory because the latter two intrinsically produce harm while any harm arising out of the former is attributable primarily to societal "homophobia." Such an argument is based on false premises and inaccurate information.
First, as we have noted above, male homosexuality and female homosexuality both produce higher rates of measurable harm but do so differently and in a manner that corresponds to male-female differences. It is thus not possible, in my view, to blame the lion's share of problems on so-called "homophobia." Incidentally, what would "incest-phobia" or "polyphobia" be and to what extent does societal disgust for these behaviors trigger higher incidences of measurable harms?
Second, there are no scientific studies demonstrating intrinsic, scientifically measurable harm for adult-committed incestuous unions, much less traditional polygamous unions. Oprah Winfrey, an American cultural guru, had on one of her television programs a year or two ago a group of intelligent, attractive, wealthy women in polygamous relationships in Arizona. By the end of the program Oprah was telling viewers that society might be painting with too broad a negative brush the phenomenon of polygamy. Even as regards pedophilia, two APA studies have indicated (one argued, the other conceded) that a child who has sex with an adult often grows up exhibiting no measurable harm. If that is true of pedophilia, how much more of adult-committed incestuous and polyamorous bonds?
After hearing a reasoned case for why homosexual practice of an adult-committed sort is more like adult-committed incest or polyamory than the conditions of race or gender, most avid supporters of homosexual unions will express great outrage. However, outrage is not a substitute for reasoned argumentation, though the former is often practiced with great effectiveness by those promoting a homosexualist cause. It might be time for those who have good arguments for believing that homosexual practice not be endorsed by society to become equally outraged.
Nor is it "hateful" to make such an analogy, unless one wants to argue that it is acceptable to hate and do physical harm to persons who engage in adult-consensual polyamorous or incestuous relationships. Love can only be exercised rightly when based on correct knowledge. If indeed incest and polyamory are closer analogues to homosexual practice and transgenderism than are race and gender, then it can hardly be loving for society to provide incentives for such behavior through "sexual orientation" and "gender identity" laws.