I very much wanted to reply to this, but it turns out that the homophobic science fiction author does not allow anyone other than his own LiveJournal friends to post comments in his LiveJournal (at least not anymore, after the criticism that his recent homophobic screed apparently attracted). So I'm posting my reply here instead. This is what I very much wanted to say:
I believe that organs can have more than one proper function. For example, one proper function of the tongue is to taste; however, this does not make it improper to use the tongue also to speak. The tongue has evolved specifically to be able to fulfill both purposes. Furthermore, although the tongue has not necessarily evolved for the specific purpose of kissing, I see nothing "objectively disordered" about using it for that purpose as well. It is a perfectly valid purpose that I suspect (without knowing the slightest thing about you, without even having so much as glanced at your LiveJournal profile) you have frequently used it for yourself. Using a tongue for this purpose makes many people happy, helps them feel more closely bonded, and does no harm whatsoever to anyone.
In the same way, I believe that the organs you call "generative organs" have evolved to fulfill more than one proper function - the functions of reproduction and of physical pleasure. The vast majority of people in the world have frequently used their "generative" organs for pleasure without intending to conceive a child. This includes masturbation, any form of non-coital sex, coital sex involving any form of birth control or infertility, coital sex with a woman who is too old to conceive or has not recently ovulated, and so on. Practically everyone in the world does these things. Sex with a member of the same sex is not different. A permanent monogamous relationship with a member of the same sex does tend to preclude reproduction, but no more so than Catholic priesthood or nunnery does, or the marriage of a man to a post-menopausal woman, or the marriage of anyone to an infertile person, or the decision of anyone to remain childless - and I don't see the Catholic Church proclaiming its own priests and nuns to be "objectively disordered."