George's Kantian Argument Against Homosexual Behavior

I haven’t done the research to really figure out the origins of this argument, though I have my suspicions that it stems from Germain Grisez.  I’ll check later.  I’ve previously called it a Kantian argument for obvious reasons, but it’s possible that it stems more from a Personalist perspective.  Dunno.

This argument can be found in In Defense of Moral Law, ch. 9, sec. I.  George and Lee also use this argument in Conjugal Union and Body-Self Dualism in Contemporary Ethics and Politics.

Here’s the argument: 
It is wrong to use a human as a mere extrinsic instrument.
Humans are identical to their bodily selves.
In a sexual activity, the body is striving towards bodily union, but the intentional mental act in a masturbatory practice is to use the bodily act as an instrument to strive towards pleasure.
Homosexual acts are a masturbatory practice as no bodily union is possible.
So both in masturbation and in homosexual acts one is using one’s body as an instrument.
So one is using a human as an extrinsic instrument in these acts.
So these acts are wrong.

More research needs to be done on why, exactly, it’s wrong to use a human as a mere extrinsic instrument and why masturbatory practices are examples of this sort of use.  Lee and George seem to suggest in parts of the argument that only a unitive striving towards a real good can unite two people into a single subject, thus avoiding using one another as a mere means.  I might follow up on that line of thought later.

One positive aspect of this argument is that it coheres well with our language and protests surrounding people being “merely used” for pleasure in sexual acts.  Anyway, here’s a link from SEP on the topic: https://plato.stanford.edu/entries/persons-means/