[YeGoblynQueenne]

>> But if general AI is physically impossible, how does the human brain "compute" general intelligence at all?

Who says that the brain "computes" general intelligence? We don't know enough about the brain to know what it is, but it's certainly nothing like a computer. Only by analogy is intelligence something that can be computed and the only reason we have this analogy in the first place is because we have computers. But isn't the accuracy of the analogy what we would like to know with some certainty, in the first place?

This is just another big assumption that is taken for granted: that the brain is a computational device. It seems an easy assumption to make, given all we know about computation. And yet, like you say, several generations of AI researchers have failed to reproduce intelligence with computers. Perhaps the reason for this is that the brain is not a computer, intelligence is not a program, and that's why we do not BSOD when confronted with paradoxical statements like "this statement is false".