It reduces to the following: Given X, if I could create a Y such that Y=X, then X would equal Y!

That adds nothing.

It isn't a given that it is even possible to 'copy' a brain. Why would one think it is? Does not quantum mechanics preclude the possibility of copying something perfectly at the atomic scale? Indeed, even if you could perfectly copy the 'material' aspect, you will still need to copy the configuration of electrical charges that existed at the moment of copying. This too is, from what I gather from QM, inherently impossible.

Does this preclude general AI? No. But it does demonstrate the absurdity of arguments that begin, "if I could copy the brain atom by atom, then..." as such a thing is impossible.