Anyone can be moral (or ethical) but only a passionate person can be virtuous

Thomas Aquinas was premodern but he was premodern in several ways. In some regards, we should be grateful that we have left that world behind. We should be grateful that we no longer live in a world where people believed that original sin was passed on sexually through the male. In other regards, we might feel ambivalent, for example, in that we no longer can easily believe that the world is oriented towards a single, divinely determined end. And there are other differences that we might simply regret.

Here is Thomas discussing "Whether all men have the same last end?" [I-II, Q1, Art. 7] He means by that whether we are aimed at the same last end and not, as our modern reading would imply, whether all humans have the same fate. It's an interesting question for, at first glance, people seem to have different goals in life. Indeed, we take it (correctly) that one of the great things about (real) liberalism is that it allows citizens considerable latitude in determining what the good life is for them. Thomas gives us an answer that may be compatible with that but isn't the usual one.

He begins, being a good medieval theologian, by making a distinction.

We can speak of the last end in two ways: first considering only the aspect of the last end; secondly, considering the thing in which the last end is realized.

I take this to mean that we can thing of the last end simply as something that is aimed at or we can consider it terms of the ways it is realized.

So, then, as to the aspect of last end, all agree in desiring the last end; since all desire the fulfillment of their perfection, and it is precisely in, and it is precisely this fulfillment in which the last end consists.

We might argue that we no longer believe that human beings have a given end which they seek to fulfill but I don't think that will hold. My counter-argument is an empirical one: most people seek to reach some sort of fulfillment of some end to which they feel they were ordained. Think of the notion of gender indeterminacy: the argument is made not in terms that a person can simply randomly pick a gender and go with it. The argument is always that people have some deep, inner sense of what they really are and a desire to become that. Which brings us to:

But as to the thing in which this aspect is realized, all men are not agreed as to their last end; since some desire riches as their consummate good; some, pleasure; others something else.

Gender identity would presumably fit under "something else". Thomas would be shocked, even stunned at the possibility but it's hard to think of a clearer example of people acting towards the end of happiness but seeing the thing through which happiness is achieved differently from others than through gender indeterminacy.

I also find it hard to imagine a project less likely to succeed. In a liberal society, however, we allow people to pick the thing that they believe will bring them happiness. That said, how do we determine what is the right answer, if only for ourselves. Here modern society has nothing to offer. We are sometimes told to look within ourselves as if there can be an answer there. Thomas's premodern answer still seems the right one to me.

Thus to every taste the sweet is pleasant but to some, the sweetness of wine is most pleasant, to others, the sweetness of honey, or of something similar. Yet that sweet is absolutely the best of all pleasant things, in which he who has the best taste takes most pleasure. In like manner that good is most complete which the man with well disposed affections desires for his last end.

We could say a lot about this. For example, "What are well-disposed affections?" In this particular instance, Thomas would likely say they are the ones in accord with natural law and go on to argue that the idea of gender fluidity is contrary to natural law. That is problematic because it involves an inconsistency in the use of natural law. Simply put, Thomas rarely uses the notion of natural law to directly derive norms in this way. Indeed, the only matter in which he (and the Catholic Church follows him in this) makes such derivations seems to be in matters of sexual morality. That sort of inconsistency tends to be self-refuting.

There is much more to Church arguments in this regard than the current culture would allow. It seems to me that if you wanted to make certain you'd be miserable, trying to live a gender identity contrary to your sexual identity is right up there with opioid abuse and divorce as a way to bring it about. But that is a different argument from simply deriving laws from some perceived regularity in nature.

The more interesting aspect of this for me, however, is how it plays out in terms of how we deal with self-mastery.

Mastery, noun
1.comprehensive knowledge or skill in a subject or accomplishment.
"she played with some mastery" synonyms: proficiency, ability, capability;
2. control or superiority over someone or something.
"man's mastery over nature" synonyms: control, domination, command, ascendancy, supremacy, preeminence, superiority;  

In the modern world, we tend to think of moral self-mastery entirely in terms of the second. Self-mastery is just an antiquated way of saying "self-control" for us. Thus the notion that we can medically over-rule our chromosomes. Far better, it seems to me, is the first definition that says we can play the roles that are given to us with mastery.

I'll stop there for now.