The only way out of the Thomistic Natural Law trap is to embrace the consistency of presuppositional thinking.
We should offer here that the secularization of the state, that Wallace speaks of is really not possible. It is true that the state, via the construct of Thomistic Natural Law, does begin to peel away from Christian precepts. However, what the state does not do when it peels away from Christian precepts, is to become “secular.” Because there is no such thing as neutrality, any state, operating by means of Thomistic Natural Law theory that peels away from Christianity will at that point begin to adhere to some other faith system, be it some form of humanism (i.e. – legal positivism, Darwinism, postmodernism, etc.) or be it some other explicit heathen religious organizing motif (Sharia, Noahide, principled pluralism, etc.). Secularization is not possible because as the State becomes less informed by explicit Christianity it correspondingly becomes more explicitly informed by some other religion.
This explains why invoking Natural Law is merely the means by which a competing religion invokes the idea of “secularization.” By invoking Thomistic “Natural Law,” a transitional bridge is built between the religion that was previously characteristic of the social order and the new religion that will eventually become characteristic of a social order as now informed and conditioned by the new religion pushing for allegiance to Thomistic Natural Law.
After all, the philosophical “natural law” had originally been of pagan origin, of Stoic origin to be precise, and had developed in the post-Alexander Hellenistic era to give rational justification for developing cosmopolitan empires.
So when the Enlightenment philosophes began to preach an openly godless version of natural law, they were indeed, in a sense, just taking back what belonged to them, sweeping away Christian additions and appendixes from that theory:
https://archive.org/details/enlightenmentint0000unse_i6k5/page/322/mode/2up?view=theater
“The image of a bridge is helpful but incomplete; it fails to evoke the essential hostility between eighteenth-century religion and eighteenth-century secularism: the philosophes rudely treated the Christian past rather as Voltaire treated the plays of Shakespeare – as a dunghill strewn with diamonds, crying out to be pillaged and badly needing to be cleaned out.
…
Hence the philosophes – rogues that they were – could claim that they were doing to the Christians what the Church Fathers had claimed they had done to the Greeks and Romans: they were merely taking back what had originally belonged to them.
This philosophic estimate is uncharitable, positively unchristian; still, here as so often before, we encounter the curious duality of the Enlightenment’s historical verdicts: the philosophes were ungenerous and prejudiced and still right in substance. What the philosophes took over from Christian theologians and Christian philosophers were the least distinctively Christian, the least religious, parts of their teachings – they were usually ideas that had come to the Church Fathers from the Stoics.”
The secularization of natural law began to really show up in Hugo Grotius (the great Arminian spokesman) – Grotius had like one foot still in the Christian past, and another foot in the impious Enlightenment, a classic transitional figure:
https://en.wikipedia.org/wiki/De_jure_belli_ac_pacis
“One of the most famous and controversial claims in the book is found in Prolegomena, section 11:
“Et haec quidem quae iam diximus, locum aliquem haberent etiamsi daremus, quod sine summo scelere dari nequit, non esse Deum, aut non curari ab eo negotia humana.”
Translated:
“What we have been saying would have a degree of validity even if we should concede that which cannot be conceded without the utmost wickedness: that there is no God, or that the affairs of men are of no concern to Him.”[12]”