CS Lewis’ writing has had a rather firm tone in his last few passages. Mere Christianity is very systematic, building up the argument for a divine Being behind the Moral Law; “The Weight of Glory” clearly but calmly denounces the kind of vainglory that we oftentimes seek. However, in “The Poison of Subjectivism,” he seems to simply be fed up with the supposedly destructive moral subjectivism pervading society.
From his point of view, “Out of this apparently innocent idea comes the diseases that will certainly end our species (and, in my view, damn our souls) if it is not crushed; the fatal superstition that men can create values.” And indeed, Lewis may very well be right. In a sense, we are playing God by adhering to such a school of thought, believing that we hold the reins of justice, morality, and even sin in our own hands. Our reason can lead us down so many different paths by merely observing reality around us, making it a shaky foundation to base absolute truth on. Surely when one person says that “abortion is wrong,” and the other that “abortion is right under certain circumstances,” one of them must be right and the other wrong. In such ambiguous cases, where two opposite views can ostensibly be justified, it would seem that something higher up than our personal reason is governing the “right” and “wrong” of a situation, as Lewis discusses in Mere Christianity; as a result, one cannot assume that they can make the moral law for themselves, and must be in tune with this Moral Law to determine what is just.
The real danger, as Lewis describes it, is that we will begin to start justifying anything and everything if we believe to heavily in moral subjectivism. As he notes, “Unless there is some objective standard of good, […] then of course the Germans are as competent to create their ideology as we are to create ours.” There are definite rights and wrongs, and they must not be bent around to accommodate our own views (or Hitler’s views). Because we are fallen creatures, our reason cannot fully discern the world and its intricate patterns of justice and morality, and therefore we must adhere to Something separate from the human world. Indeed, “Unless the measuring rod is independent of the things measured, we can do no measuring.”
Thus, in playing God by inventing new morals for humanity (such as “all religions lead to heaven”), we are treading in dangerous waters, since we are dealing with a God who created the Moral Law and who also does not change, unlike us. How, then, can we expect that morality can evolve in such circumstances? As Lewis says, “All idea of ‘new’ or ‘scientific’ or ‘modern’ moralities must therefore be dismissed as mere confusion of thought.”