The Abolition of Man is absolutely essential because it gets to the core of what I feel is the only debate worth having at this stage of history. Lewis is talking about First Principles in the context of classical philosophy. Every claim comes prepackaged with its own ethical, epistemological and metaphysical presuppositions.
Despite his own Christian beliefs, he’s taking an ecumenical approach to time honored wisdom. If you are going to strip away all traditional notions of duty, honor, virtue in favor of a more “natural” approach to Man, then you consign Man’s soul to the meat grinder of the scientific data mill. Thus making subsequent generations slaves to the scientific class who are going to condition the masses to accept whatever definition of “good” is going to be most expedient to the larger goal of consolidating power within the scientific priesthood.