Post implies that natural science is lending ever greater support to a theory of being qua being. For me this is a fundamental mistake. I fail to see how any amount of natural-scientific investigation could decide between competing theories of being qua being. But before I provide my reasons, let's consider another reason Post gives for the attractiveness of physicalism:
A fourth reason is that, unlike most other theories of being qua being, physicalism is meant to be criticizable by way of observational testing. According to contemporary physicalists, the principles of physicalism are to be treated as high-level empirical hypotheses or generalizations.
What Post is saying, then, is that the metaphysical proposition
1. To be is to be physical
is an empirical generalization supported by natural science and open to disconfirmation by future experience. Three objections immediately come to mind.
Objection One
The gist of my first objection is that (1) cannot be an empirical generalization. Empirical generalizations, if true, are contingently true. So if (1) is an empirical generalization, then (1) is contingently true. But then it can't be the case that to be is to be physical.
Why not? Well, (1) asserts an identity between the 'property' of being (existence) and the 'property' of physicality. This identity entails the necessary equivalence
2. Necessarily, for any x, x exists iff x is physical.
(One cannot validly move from equivalence to identity, but one can validy infer an equivalence from an identity.)
The upshot is that (1) is both contingently true (because it is an empirical generalization) and not contingently true (because it entails a necessary truth). But this is a contradiction, so (1) is not an empirical generalization.
Once one appreciates this, one sees that physicalism cannot be supported by natural science. In general, metaphysical propositions about being qua being cannot be supported or refuted by naturalistic methods. Natural science cannot take the place of first philosophy.
But couldn't (1) be taken to assert the contingent identity of existence and physicality? I don't see how. Indeed, I have no idea what that could mean. If two individuals are identical, then that is necessarily the case. Contrapositively, if two individuals are possibly distinct, then they are distinct. Similarly, if two properties are possibly distinct, as they would be if they were only contingently identical, then they are distinct. Consider a possible world in which something exists that is not physical, the number 9 say, or perhaps some set of physical objects. In that world existence and physicality are distinct properties. But if they are distinct in one possible world, then they are distinct in all possible worlds, including the actual world.
Second Objection
My second objection is that (1), if true, supplies itself with a counterexample, and thus refutes itself. (1) expresses a proposition, call it P. (I take it to be self-evident that a proposition must not be confused with its physical embodiment whether it be marks on a page or pixels on a monitor.) So if (1) is true, then the proposition P expressed by (1) is physical. But there is no tenable theory of propositions according to which propositions are physical entities.
Frege's Gedanken, for example, despite their name, are Platonic entities and therefore nonphysical. The same goes for Bolzano's Saetze an sich. Suppose you say that propositions are not Platonic entities but exist only as the accusatives of judging minds. Still, such accusatives cannot be intelligibly viewed as a physical entities. They are senses, even if they cannot exist in splendid Platonic independence. Less plausibly, a proposition might be construed as some sort of set-theoretical construction, whether a set of utterance events or a set of possible worlds. But even these far-fetched theories don't help since sets are abstract entities, hence nonphysical.
Propositions, then, cannot be physical. So (1), whether true or false, expresses a proposition, a nonphysical entitiy. Therefore (1) is false: the proposition it expresses is its own counterexample.
Third Objection
My third objection is a circularity objection: (1) is damagingly circular. To see this, ask yourself whether Pegasus is a counterexample to (1). Pegasus is a winged horse. So Pegasus is a physical item. After all, a horse is a physical item, and to add physical appendages to a physical item does not alter its physicality. So Pegasus appears to be a counterexample to (1): Peagasus is physical, but does not exist. To block this and like counterexamples, one must construe (1) as short for
3. To exist = to be physical and exist.
On this construal, (1) is true but circular. This shows that existence cannot be identified with the categorial property of being physical. Indeed, it shows that existence cannot be identified with any property. And this for the simple reason that nothing can have a property unless it exists.
Conclusion
Physical science studies physical reality. But it is in no position to establish that physical reality exhausts the whole of reality. The assertion that to be is to be physical is a meta-physical assertion in that it attempts go beyond physical reality to characterize reality as such. My second and third arguments show that this meta-physical assertion is false, and my first argument shows that it cannot be supported by natural science.
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4. Some undesirables: The skimmers, those who cannot read but only read-in. The sophists who, abusing argument, argue for the sake of argument. The ideologues, those who are out for power, not truth. The uncivil. The illogical. The politically correct. Worst of all, perhaps, are those who exemplify the anti-Socratic property: those who think they know what they don't know. If Socrates was famous for his learned ignorance, these types are marked by their ignorant unlearnededness.