I'd call it sf, sure, but have no problem with someone wanting to uphold a more restrictive definition of sf than mine that would exclude this. But if I were still teaching, and were putting together a science fiction elective, I might well include this as an assigned text.
It's a while since I've read it, but my memory is that the father talks to the son about being a person of the fire, meaning some spiritual principle or inner presence. The sense I got was definitely not of a Christian outlook, but of a Gnostic one: there are fleshly people, not redeemable, and who belong in a dark world like this; but here and there, there are spiritual people who do not belong in this wretched material world in which they are "caught." The task of the spiritual is to realize what they are and endure this dark world till they are reunited with the world of light from which their being derives. There's nothing in the book that spells all this out, and I don't mean I think McCarthy is a Gnostic plain and simple; but that, it seems to me, is the character of his imagination in this novel at least. If I'm right about this tendency, then the "hope" in the book is not that somewhere people will start civilization over again, etc., but that the boy has found other bearers of the light, his proper people, and whether they live for years yet or not is not really the point. They know they are creatures who do not eat people.
The sense I get is that the catastrophe of the "shear" effects an apocalypse in the literal sense of that word, i.e. a revealing, an unveiling, of the way things really are.
