"it implies that among two systems with absolutely identical external behavior in all respects, one can have conscious and the other not have it." That stateme

"it implies that among two systems with absolutely identical external behavior in all respects, one can have conscious and the other not have it." That statement can be true without being metaphysical. You can't treat a human as a black box, and then use inputs and outputs to definitively draw conclusions about what's going on inside the black box. You could potentially have two black boxes that give identical outputs for the same inputs, yet have completely different mechanisms inside for arriving at those outputs. For example, say you have someone who's very good at arithmetic able to multiply two numbers. You put him inside one black box and a pocket calculator inside another. You give each box two numbers and they both output the product. Both black boxes will give you identical outputs for any given input. You know the box with the person inside is conscious, but this is not enough information to conclude the other black box is conscious. It's quite possible that there is a way to simulate human behavior through some other non-conscious mechanism. And just because we can't currently prove whether something is conscious doesn't mean it's something metaphysical we'll never be able to prove. For example, if two people tell you they're experiencing some pain, but one is lying about it, a few hundred years ago you'd be unable to prove it. That didn't mean pain is something metaphysical. Today, we know it might be possible to put both people in an MRI and prove whether they're actually feeling pain