Bealer has a number of reasons for thinking that a naturalistic epistemology is self-undermining. Let me focus on one of these. (I've tried to take on all of them in the first chapter of Knowledge and Its Place in Nature.)

In my view, since the case can be made that knowledge too is a natural kind, the role of pretheoretical intuitions is similarly diminished in epistemology.

One of the goals of scientific theorising is to develop concepts which are adequate to the phenomena under study. In my view, things should work the same way in epistemology. We want to know what knowledge actually amounts to, not what our folk concept of knowledge is, since, just as with our pretheoretical concept of acidity, it might contain all sorts of misunderstandings and leave out all manner of important things.

I do realise that talk of natural kinds dates back to Aristotle, but I'd better not say too much about ancient philosophers lest I be convicted of practicing history of philosophy without a license.

What I hankered for was an account of knowledge which would do far more than get our intuitions about cases right; I wanted a kind of account which would somehow be explanatory.

There is a worry that many have expressed that, on the naturalistic way of approaching philosophical questions, philosophy will somehow be co-opted by science. I'm not much worried about this.

No one would suggest that we can adequately investigate what makes something an acid, or what makes something aluminum, by bringing our pretheoretical intuitions about these things into reflective equilibrium by way of armchair theorising.