Is homosexuality ethical? If so, what differentiates it from incest? More specifically an infertile incestual relationship that has two consenting adults.

An interesting question. To answer in order: Homosexual relationships, like heterosexual relationships, can be conducted in both moral and immoral, virtuous and vicious, ways. I find no reason to regard homosexuality to be itself immoral. Of course, many others, especially those with religious commitments, think otherwise.

For myself, I find that the many pleasures and virtues achieved through homosexual relationships (pleasures and virtues that would be lost to us were homosexuality prohibited) militate against judging homosexuality to be per se immoral. Besides religious objections, there are also, of course, various civic and health-related arguments against homosexuality (e.g. that it undermines the family, that it exhibits and produces illness, that it makes for incompetent parenting). So far as I can tell, these are, similarly, either unsound or outweighed by the goods produced by homosexuality.

How is homosexuality different from incest? Well of course the two are different simply by definition. Homosexual relationships are same-sex relationships. Incestuous relationships are sexual relationships among close family members (and, of course, what counts as too close varies from society to society). Incestuous relationships may or may not be homosexual. Homosexual relationships may or may not be incestuous.

What's the moral difference between (a) an infertile (heterosexual, I take it) incestuous relationship that comprises two consenting adults and (b) a binary homosexual relationship? I suppose I would say that the crucial moral difference is that the infertile incestuous relationship involves close family members while the homosexual sexual relationship (assuming it's not incestuous) does not. The moral weight here is born by the moral prohibitions built into the idea of family.

I'm not an anthropologist, but I'm told by them that every organization of family involves some sort of incest prohibition. Could there be families without incest prohibitions? I don't know, but I have my doubts. Could there be homosexual families? The existence of many homosexual families makes it abundantly clear that there can be.

I take it, however, that there's a more challenging implied question here: if homosexual relationships are morally permissible, then as a matter of consistency shouldn't incestuous relationships between infertile consenting adults be premissible, too? If we are to permit homosexuality, what grounds can there be for regarding incest between infertile consenting adults to be immoral?

As I said, it's an interesting question. Now, as I see it, incest prohibitions are indeed about preventing the biological problems rooted in reproduction involving beings too closely related. It would seem, at first blush, that this wouldn't be a risk for an infertile incestuous couple; but keep in mind it's not always certain that someone is infertile.

Moreover, those prohibitions are of course also about other things, like preventing other pathologies that empirical evidence suggests are likely to arise among siblings or even first cousins who become lovers. Again the moral work here is done by the concept of family. This may be one reason why so many critics of homosexuality wish to argue that it would also undermine "the family" or that it's inconsistent with the very idea of family.

At this point things become empirical again. Do such pathologies really exist in the case of incestuous relationships but not in homosexual relationships? Some of those opposed to homosexuality maintain that there is empirical evidence to support the claim that homosexuality produces and exhibits various pathologies, physical, mental, and social. I've not been persuaded that this is so. My personal experience suggests that homosexuals are able to participate in all of the goods produced by heterosexual relationships, except of course breeding. The vices they commonly produce seem comparable to those of heterosexuals, as well.

In addition, neither the American Psychological Association nor the American Medical Association find homosexuality to be pathological. On the other hand, my guess is that the APA would regard incestuous relations even among infertile consensual adults to be pathological.

Of course, they might be wrong in this. The APA used to regard homosexuality as pathological. Then after reconsidering the issue, it changed its position. Again, incest taboos are rather plastic across cultures. Perhaps we might relax the taboos against incest in situations like those you describe, so long as they can be shown to be harmless. If you could show empirically that incestuous relationships among consenting infertile adults (a) do not exhibit or produce psychological, physical, or social pathologies and (b) infertility can be conclusively established in such cases, then you'd have a good start on arguing that the practice is morally permissible.

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