This is for the scholastic philosophers, those who follow in the footsteps of Averroes and St. Thomas Aquinas.
Consider the mouth. Its final cause is to eat, allow us to breathe and serve as a means of communication. There is no doubt at all that this is its purposes, from how it functions and from the tongue’s construction, and its shape.
Consider also the genitals on a man. There is no doubt that’s its final cause is to deliver sperm into the vagina of a female. It is made quite well and integrated with the human body of a man to do just that.
Yet at the same time it seems I can use my mouth for other things, than what it is ordered towards. I can use it to hold nails. I can make music with it by whistling. I can even store things inside of it, if I feel inclined to. I can use my tongue to count along my teeth. Etc, etc… It seems that I can always use my intellect to use my mouth for purposes it isn’t specifically ordered towards, and none of these are in any way the primary use of the mouth, but that doesn’t make doing any of these morally wrong.
Likewise a mans genitals, can in fact be used to sexually stimulate another man. This produces a mutual pleasure, which is quite enjoyable, subsumed within a desire to make the other one feel well. This is not the primary purpose of the genitals. They’ve subverted the intended purpose of the penis, and this doesn’t appear to be different than the case with the mouth.
Yet why is it not morally wrong to hold nails with the mouth, whistle, count on your teeth or blow up balloons. But it is wrong for two men to sexually stimulate each other with their genitals.
I expect an objection: Some might point to scriptures and tradition. God threatens infinite pain if you do one thing, but He doesn’t threaten infinite pain if you do the other. I agree with that. But I’ll ask you to count out scripture and tradition here. I am not talking about consequentialistic ethics here. I’m talking about the virtue based ethics of scholasticism.
Argue as you would argue with a deist, who doesn’t believe in the Catholic Church: Why is it okay to whistle and hold nails with the mouth, or otherwise subvertive purposes, but it is wrong for two men to use their genitals to please each other?