Thanks for the link. Aquinus, being a philosopher, attempts to explain the hidden by using what is observable. This was a kind of forerunner of Science, to use arguments to extract hidden truth from observable truth. This is in accordance with the belief that everything that can be known about God can be known through nature. Aquinus was at a disadvantage to us who have microscopes unless we believe that microscopes yield no additional information about God. Also he approached homosexuality as a pleasure that came from the corruption of purpose, but he did not know apparently that people can be born homosexual. Perhaps he had one hand tied behind his back trying to explain his opinions using only natural principles and the limited information at hand.
The article (but not Aquinus) proposes that 'The sex act' has a unitive purpose and projects this unstated opinion onto Aquinus. Why put words into his mouth that he did not say? Convenience? Where does this argument come from? Aquinus does associate homosexual acts with breaking the 6th commandment, but why? The article says its because Aquinus 'Must have believed' sex had a unitive function. That is objectionable. In the first place it could be argued that marriage has the unitive purpose, not sex. Why must sex have a unitive function? If so, then why is marriage needed? What if I can provide an example, in the Bible, of sex with reproductive but without unitive function between a prophet and a prophetess? What if in nature I can provide an example of sex with apparently neither reproduction nor union? So what we have is Aquinus saying that he thinks homosexuality breaks the 6th commandment, but we don't have a naturalistic explanation from him.
From what natural principle comes this supposed unitive purpose for sex? Is it not an opinion imposed upon nature?
A Eunich has or should have a place in Christianity I think with no less honor or importance than someone else. The article agrees and says "The celibate lifestyle to which those with a permanent or irreversible condition of homosexuality (if there is such) are called need not be lonely and isolating. There are many, for instance, celibate priests, nuns, and laypeople, who forgo the intimacy of marriage, sexual relations, and family." So then what happens to the unitive purpose of the sex organs of celibate priests, nuns and laypeople? It is left unused, put to no use at all neither for friendship nor for pleasure. How is that natural?