That's fine, except that quantum mechanics messes with the idea of determinate physical causation, and the Free Will Theorem (as well as the KS Paradox that it

That's fine, except that quantum mechanics messes with the idea of determinate physical causation, and the Free Will Theorem (as well as the KS Paradox that it extends) is based on a particular proof that certain things (in this case, the measurement of the spin of a particle under certain circumstances) do not follow physical causation. What the FW Theorem shows is that if you take a situation in which we assume humans have free will, then the result is that subatomic particles also have that exact same kind of free will.