Not a bad argument, but a bit metaphysical for people looking for a logical reason "why not?"
The reasons "why not" are straightforward: diseases that spread in almost no other way, greatly increased risk of sex act-incurred physical damage to one or both homosexual partners, the impossibility of reproduction in such relationships, the confusing and unhappy role models for children that homosexuals inevitably become, and the societal damage caused by the promiscuity inherent to the lifestyle. Every single one of these objections is logical, reasonable, intellectually sound, and applicable whether one is religious or not (though gay advocates will fight them all to the death - mostly with lies and false statistics aimed at distorting the truth).
And not one of them depends on the existence of some mean guy with a white beard up in the clouds who is going to smite homosexuals with lighting bolts unless they give up their practices. ;)
True, but the person who asked him the question already is a believer, so...
It seems perfectly reasonable as well to question the sanity of males who refer to themselves as "queens," "bitches," and certain female genital parts, as well as the sanity of the males who obligingly refer to the former as "she and her." There is something peculiarly repulsive in hearing males speak of themselves in that way.