John Wilkins explains the reason he is a physicalist:
When I lost my belief in religion I had to decide what I needed to accept as a bare minimum. I decided that I needed to believe in the physical world. I never found the slightest reason to accept the existence of anything else. To this day I am a physicalist only because I never found the need to be anything else.
The principle of parsimony suggests that one should not believe in more than one needs to. Even if it does make you feel comfortable.
There are many reasons why someone would be a physicalist (John himself gives others), but this one is complete and absolutely fundamental. There simply is no reason behind this one, or at least there need not be. After this, physicalism can fall back into the defensive activity of answering various objections- it need not seek to do any more to establish itself in a positive way. If we tried to push the analysis any further back, we would slip into the non-rational sphere of personal and somatic characteristics, the infinite ocean of the subconscious, and the dark causality of whatever else there is.
My fundamental reason is the contrary of Wilkins. His challenge was to believe as little as possible, mine was to believe in the greatest thing possible. His fundamental outlook is critical and minimalist, my fundamental outlook is to find the greatest or loftiest thing that I can. He appeals to parsimony, and there is also a clear implied appeal to certitude; my appeal is to the natural desire to seek what is highest and most perfect. He takes it as obvious that one should never posit more than he needs to; I take it as equally obvious that no one would ever settle for the merely necessary and minimal. He might well see my choice as wishful thinking or a naive uncritical approach that could leave me duped in a thousand ways; but I see his as choice as mean, scrupulous, and closed- minded. His appeal is to Ockham’s razor, mine is to Aristotle’s dual axioms that what is most perfect in itself is least knowable to us and that we cannot but seek the beatitude that comes from knowing what is most perfect in itself.
To put it in a word, John sees everything beyond the minimum given in initial experience as a threat to philosophy, and even as unphilosophical; I see the whole point of philosophy as finding some object beyond this minimum given in initial experience.
I don’t know that there is any possibility of rapprochement here, or even if either of us can critique the other in light of a principle we both accept. By our own lights, the other is committed to irrational and even anti-rational beliefs, and it’s hard to see how we could account for this by saying both of us are working from some common understanding that the other guy is misinterpreting. This is particularly striking in John’s claims about the self – we both see that (his?) physicalism requires that the unified human self be an illusion, but he takes this as a philosophical proof for the impossibility of a unified self and I take it as a reductio ad absurdum against physicalism. For him, “the (unified) self” is an objection that he can solve by an appeal to semantic constructions, to me it is a starting point for what will count as a being.