Part 2: What Disproportionately High Rates of Harm Mean
At the very end of Part 1 I noted that homosexual intercourse, like incest, is problematic because of the excessive embodied (formal, structural) sameness of the participants; moreover, that problems with procreation for both incest and homosexual behavior are merely symptoms of this root problem of excessive structural identity.
We need to go further; for problems with homosexual activity are not limited to a structural inability to procreate. Homosexual relationships also exhibit a disproportionately high rate of scientifically measurable harms. These measurable harms cannot be explained away as merely a product of societal "homophobia" but are instead largely attributable to the lack of true sexual compatibility (or complementary symmetry) between persons of the same sex.
If the disproportionately high rates of measurable harm manifested by homosexual relationships were attributable exclusively or even primarily to societal "homophobia," then we would expect male-homosexual relationships and female-homosexual relationships to exhibit the same high rates for the same types of measurable harm. However, this is exactly what we do not find.
Homosexual males experience disproportionately high numbers of sex partners over the course of life and of sexually transmitted infections, not only in relation to heterosexual males but also in relation to homosexual females. The reason for this is not difficult to imagine. On average men have 7 to 8 times the main sex hormone, testosterone, than do women. That has an obvious impact on male sexuality, relative to female sexuality, such that bringing together two men in a sexual union is not exactly a recipe for monogamy. Incidentally, the polysexual character of male sexuality has been shown scientifically to be not only a cross-cultural phenomenon but also, to a large extent, a cross-species phenomenon.
As regards lesbian relationships, the limited studies that we have to date suggest that homosexual females experience on average disproportionately high rates of measurable harm as regards shorter-term sexual relationships and higher instances of mental illnesses associated with such relationships, relative not only to heterosexual females but even to homosexual males.
The issues around lesbian mental health are not surprising in view of the fact that on average women have, relative to men, higher rates of mental health issues and higher expectations of sexual relationships for meeting needs of self-esteem and intimacy. Simply put, failed sexual relationships place greater stress on women's mental health than on men's. I trust that most people recognize that women on average have much higher intimacy expectations for sexual relationships than do men. This is why, almost invariably, in a marriage between a man and a woman it is the wife who complains that her spouse doesn't share his innermost feelings often enough. "Men are from Mars, women are from Venus," as one marital counselor has famously put it.
The matter of shorter-term unions on average at first seems counterintuitive since women generally do better in being monogamous than do men (this is true also of lesbian women in relation to homosexual men). However, the fact that women have higher expectations for sexual relationships as regards meeting personal needs for security, affirmation, and intimacy places greater stresses on such relationships. When two women are put together in a sexual union, each making great demands of the other, stress is heightened and the likelihood of relational failure increases.
In short, the disproportionately high rates of measurable harm attending homosexual relationships strike homosexual males and homosexual females differently and do so in ways that correspond to basic sexual differences between men and women. When two persons of the same sex are brought together in a sexual union, the extremes of a given sex are not moderated and the gaps in a given sex are not filled. On the level of anatomy, physiology, and psychology a man's appropriate sexual complement is a woman and a woman's true sexual complement is a man.
Like homosexual practice, both incest and polyamory exhibit disproportionately high rates of scientifically measurable harm, not intrinsic, measurable harm. Because of close family structures incest often occurs between an adult and child, though it does not always, and need not, manifest itself in this form. In addition, if procreation arises from an incestuous bond, there is the additional problem of a higher risk of birth defects. Neither problem constitutes an intrinsic harm stemming from incestuous bonds but each involves increased risks attending societal affirmation of close-kin sexual relationships.
Polyamory increases the risks of promiscuity (if by promiscuity one means something like "one-night stands" rather than long-term relationships), domestic jealousy and discord owing to multiple spouses, and (in traditional polygamous relationships where only the man is allowed multiple spouses) overbearing patriarchy. As with incest, we are dealing with increased risks, not inherent harms. There undoubtedly are some polygamous relationships that "work" better than some monogamous relationships. As with homosexual relationships, the disproportionately high rates of measurable harm are not the problem per se (as if the absence of measurable harm would justify the relationship's existence) but rather symptoms of the root problem.