Other objections aside, here is the real problem with Naturalized Epistemology as I see it. On the one hand, the principle motivator for adopting Naturalized Epistemology is the view of Metaphysical Naturalism (which is what is most often called simply ‘Naturalism’, by which I understand the general claim that “nothing exists apart from all the objects, entities and forces postulated by physics and/or those which would be postulated by the most comprehensive physics“), and on the other, adopting Naturalized Epistemology does not marry one to Naturalism. One can adopt a Naturalized Epistemology, according to which one should only believe in entities which our preferred empirically adequate theory postulates, and not end up with beliefs which fall within the orbit of Naturalism. Since Naturalized Epistemology presumes that there is no first philosophy, that foundationalism is untenable, and that, as Quine himself (the father of Naturalized Epistemology) put it, “the stimulation of his sensory receptors is all the evidence anybody has had to go on, ultimately, in arriving at his picture of the world” (Lukas Graf, Theories of Knowledge), its presumptions seem to be the deliverances of a radical empiricism which is a concomitant of Naturalism. Naturalized Epistemology begins by presuming Metaphysical Naturalism or something very much like it (I’m inclined to think there is no difference between Naturalism rightly construed and the idealism Hume inherited from Berkeley, which is just wholesale and consistent empiricism), but quickly leads one to believe in the existence of things which fall outside the boundaries of what is usually called Naturalism. For example, W.V.O. Quine himself was led to postulate and believe in the existence of sets. It isn’t hard to imagine a Naturalized Epistemologist finding similar impetus for postulating God, or a being very much like ‘God’. So, Naturalized Epistemology begins by presuming Naturalism, or something very close to Naturalism (depending on how Naturalism is construed), and may end just about anywhere, including Theism (I take it that there is hardly any view more remote from Naturalism than Theism).
Now, I believe that Naturalism is clearly false. I can think of no good arguments for its truth, and I think the attraction to it has been eroded by philosophical developments in the later part of the twentieth century, among them being the dismissal of the chronological snobbery of scientistic optimism; it is no longer a very popular prejudice to have. However, the Naturalized Epistemologist has to convince us of Naturalism in order to convince us that we should adopt Naturalized Epistemology, and yet, if we were to adopt Naturalized Epistemology, we may plausibly end by rejecting Naturalism altogether. Who would retain Naturalized Epistemology if they were no longer a Naturalist? Why?
So, Naturalized Epistemology seems completely unattractive to me; nevermind that I lean towards rationalism contra empiricism, nevermind that I think we intuit logical and mathematical truths along with some metaphysical truths, nevermind that foundationalism seems plausibly tenable to me, the real point is that Naturalized Epistemology finds its home in Naturalism, but may reach beyond the borders of Naturalism and force it’s adherents to postulate any number of entities which are not ‘naturalistic’. The epistemology makes too many metaphysical (or otherwise philosophical) assumptions, and then doesn’t guarantee those assumptions against falsification.
This is the fatal, singularly unattractive flaw of Naturalized Epistemology; in a market place of ideas it isn’t likely to be bought by anyone who isn’t a Naturalist already, and it may easily push its adherents beyond the borders of Naturalism (making it possibly and easily self-defeating unless one either constrains it more tightly by metaphysical assumptions, or defines metaphysical naturalism so broadly as to make no view ‘in principle’ opposed to it).