Actually, the more I think of it, I think the causal-closure principle often trades on an equivocation. We can speak of the “physical” in two senses:
Physical A: pertaining to being qua changing, to physis broadly construed; or
Physical R: pertaining specifically to microphysics.
I think there is often a (perhaps unintentional) equivocation using the plausibility of A to assume R. When it comes to questions of agency or the causal efficacy of life forms, etc., R is simply question-begging.
Now, a common point here is that “physical laws” are never violated at different “levels.” Which is true, but is merely a tautology, since regularities are only considered “laws” when they are never violated (or if they are shown to be consistently violated, we just change them). Similarly, laws of chemistry or biology, when defined the same way, are by definition never violated. And at any rate, the move from “physics is never violated” to “physics is explanatorily primary” is a non-sequitur.
Now, if a metaphysics cannot tell the difference between a man and a corpse, I would say it is defective. I am not sure how one gets this from particle ensembles or fields if “higher levels” are assumed to be causally inert. But even if we grant that some real morphism could be identified where all living things can be identified in terms of something like particle arrangements, this would still simply be a morphism that is defined by reference to the biological category it’s supposed to reduce. Coextension is not reduction however. The mathematical characterization would still be parasitic on the biological concept, barring some sort of actual grounding relation. Really, it would simply be an extensional definition that manages to invert the place of the principle that unifies all of its instantiations, and the contingent instantiations of said principle–a bit like defining a frog by piling every frog in the world into a heap. But extensional definitions are all the rage (even validity is often defined this way, or necessity, as sheer frequency), and I think this ultimately traces back to nominalism.
Which I mention because nominalism offers another problem here. Supervenience would seem to assume some sort of composition relation, but within physicalism it seems that composition often is extremely fraught (universalism and nihilism being quite popular). Often, it is said that composition is wholly defined in terms of what we currently find “useful.” To be sure, there is commonly a pivot to functionalism here, but since teleology is also often excluded, “function” is just as often considered arbitrary or illusory. But talk of supervenience re higher and lower levels or parts and wholes with arbitrary composition is going to be hamstrung from the outset. In particular, if all “higher level” natural kinds/wholes are causally inert (because the physical “base level” is causally closed), then in virtue of what are there any meaningful wholes/levels by which to define supervenience in the first place? More to the point, even if these “levels” could be defined in terms of epiphenomena, those epiphenomena cannot, by definition, explain our act of embracing those definitions (making our very philosophical language inexplicable).
This is painfully obvious in Kim’s exclusion argument because he has to define B-minimal properties in terms of mental states, which, according to his own theory, are causally inert. So, P1 is only called P1 because it produces M1, but M1, containing the thought “P1 is the cause of M1” can never be the cause of us identifying P1 as the cause of M1. Yet the pivot to reductionism/identity theory doesn’t actually resolve this issue, since it still implies that the existence of M1 isn’t the cause of us talking about M1 (which just highlights the accidental relationship between the two highlighted in my first post).