Let’s set aside Fr Spitzer’s error-riddled book to focus on Catholic Answers’ article. If you really want my opinion of it, I will try to publish my 14-page refutation of Spitzer on Amazon at a later date (and charge some 14/400 of what he charged for his 400 pages).
I think demonstrating Catholic Answers’ argument to be unsound can be done more simply by disagreeing with a different premise and implicit assumption: “Cat” is not clearly a form that exists spiritually to be ‘dependent on’ or ‘conditioned by’ cells for its existence physically, nor are “cells” a form dependent on molecules for their existence, etc. Rather, the cat is a collection of cells, those cells are collections of molecules, etc. When we recognize that the word ‘cat’ is simply a euphemism or label for a particular collection of cells, etc., we see the basis for Aquinas’s metaphysics vanishes: It is nonsense to speak of molecules “giving their existence to” cells, and cells “giving their existence to the cat”, or equivalently, “cells depending on molecules for their existence”, because the cat is those cells; the cells are those molecules; the cat is those molecules. It doesn’t “depend” on them: It is them. Do you depend on yourself for your existence? No, you are yourself.
Moreover, the cat – or any other object – is conditioned only by things external to it. Hence if its mother eats well while pregnant, the cat will be born healthy; frail if she doesn’t. The cat’s location is conditioned by my attention and my water bottle.
So the entire article is really a misuse of words. It is an attempt to present the argument from contigency by redefining what ‘conditioning’ is and by failing to realize that we use words as labels for collections of things (e.g. cat = collection of cells; cells = collection of molecules), i.e. it implicitly makes the unjustified assumption that Aristotelian “form” exists.
Edit: Perhaps I should attribute these ‘forms’ to Aquinas or Plato, rather than Aristotle … but I hope you know what I mean.
(As an aside, a thought experiment even shows, I think, that “forms” do not exist: Suppose you have a rock that looks like a chair. Is it a rock or is it a chair? The fact that we can be confused shows that these forms only exist in our minds, not independent of them. (What actually exists are the atoms, made of calcium, etc.) Hence they were useful fictions, not observed realities, and are no longer needed now that we have modern science – and given our discovery of atoms and constituent molecules, you must justify such metaphysical models before you may use them instead of our physical models.)