Catholic and Christian principles do inform some secular subjects, such as law, business ethics, medical ethics, and so on, but only to the extent that questions of faith and morals are involved in the first place.
I think we are saying the same thing, basically. Of course various secular disciplines need to be informed by Catholic faith and morality.
Mathematics and engineering, for instance, are pretty neutral. An atheist, an agnostic, a Muslim, a Jew, or a Christian will learn the same things, in the same ways, and faith or morals do not even enter into it.
Some aspects of business most certainly do have an ethical coloration. The mechanics of manufacturing widgets are morally neutral, but the ownership of the widget factory, obtaining the raw materials to make the widgets, the rights of the employees who are hired to make the widgets, a just price for the widgets, and whether widgets are safe to use — all this, and more, requires the application of ethical and moral principles. Is it better for the widget factory to be owned by one rich man, or should many people each own a small piece of the factory? Are indigenous or dispossessed peoples exploited in the extraction of the raw materials? Does the raw material extraction conform to good stewardship of the environment? Are the widget makers paid a fair wage? Is it moral to charge whatever the market will bear for the widgets, or is there a “just price”? How do you determine it? Is it moral to allow children to buy widgets, or could they get hurt with them? You could teach a whole semester of Catholic business ethics just on that one widget factory.
Likewise with history and literature. Were they “the Dark Ages” or was it “the Age of Faith”? A bit of both? Why? Was the Protestant Reformation good or bad? The American Revolution? The French Revolution? How were they different? What were Voltaire’s ideas? Does it endanger our faith to read them? Can we accept them? How do we refute them? Marx? Lenin? Ethicist Peter Singer? Stephen Hawking’s ideas on the existence of God? Can any good be derived from Saul Alinsky? It goes on and on. A student educated in Catholic doctrinal and moral principles could spend ten lifetimes studying these ideas and concepts.
A person could do a lot worse than to take out four years of their life, get the money somehow, and go to Thomas Aquinas College (
https://thomasaquinas.edu/ ). I didn’t. Part of me wishes I had. They deal with that kind of stuff there.