We don't have to prove that the brain isn't puppeted from some external realm of "consciousness" in order to say we can be quite confident that it isn't, because positing that there is such a thing as free will in the traditional notion of the term is magical thinking, which most of us might agree isn't particularly respectable.

What we can do is take a compatibilist approach and say there is something that is "effectively indeterministic" about human decision making, because we can't ever ourselves predict our own actions any faster than we observe them. I don't have any moral contribution to make here; I just wanted to add this reflection.