Thus, if you believe that the Bible, the Torah, the Qu'uran, or the writings of the gods of secular academia contain specific instructions for the conduct of human life, instead of expressing general principles of truth that apply within a particular sphere, you tend to reject the underlying principle(s) in favor of specific applications that may or may not apply in a particular case. The problem becomes discerning the real basis for the natural law, and going from there, rather than taking your own opinion as to the meaning of some revelation, whether religious or scientific, and trying to force it on everyone else.
This is the whole point of the analysis in Dr. Heinrich Rommen's book, The Natural Law (Amazon, Barnes & Noble) written in the wake of the Nazi tyranny as an effort to explain the origins of totalitarianism. Dr. Rommen, a student of Father Heinrich Pesch, S.J., the great solidarist philosopher, was a member of the Königswinterkreis study group that included, among other notables, Father Oswald von Nel Bruening, S.J., who drafted Quadragesimo Anno ("On the Restructuring of the Social Order"), 1931, under the direction of Pope Pius XI. One of Germany's leading jurists, Dr. Rommen was forced to flee Germany in the 1930s, ending up teaching at Georgetown University, although (oddly) not at the law school. As Rommen explains the position of those who rely on faith rather than reason in matters of science (and, yes, theology and philosophy are sciences),
For Duns Scotus morality depends on the will of God. A thing is good not because it corresponds to the nature of God or, analogically, to the nature of man, but because God so wills. Hence the lex naturalis could be other than it is even materially or as to content, because it has no intrinsic connection with God's essence, which is self-conscious in His intellect. For Scotus, therefore, the laws of the second table of the Decalogue were no longer unalterable. . . . Now . . . an evolution set in which, in the doctrine of William of Occam (d. cir. 1349) on the natural moral law, would lead to pure moral positivism, indeed to nihilism. (Heinrich Rommen, The Natural Law, 51-52)This, then, appears to be the major philosophical issue of our day: whether the natural moral law (and thus the positive law) is to be based on Nature (Intellect/Reason), that is, what we can discern of divine Nature reflected in human nature . . . or whether the natural moral law is purely a matter of opinion, and whoever is the strongest makes and enforces positive law based on whatever he or she can get away with. As Mortimer Adler observed,
The denial of natural rights, the natural moral law, and natural justice leads not only to the positivist conclusion that man-made law alone determines what is just and unjust. It also leads to a corollary which inexorably attaches itself to that conclusion — that might makes right. This is the very essence of absolute or despotic government. ("The Meaning of Natural Law")So, to answer the question with which we began this series and reiterate and restate Mortimer Adler's definition, the natural law is the body of principles that guide human conduct. These principles, discernible completely through the use of human reason, are based on understanding of our own nature as we see it manifested in the behavior of our fellow man and our beliefs as to what constitutes the "good" measured against what people have in all times and places agreed is "good."