I'm currently reading Simon Blackburn's "Think", in which he claims to use metaphysics to all but explain away the idea of Cartesian dualism. He claims that if it were true that the mind is distinct from the body, that it would create the possibility for "zombies" to exist who function just like us, but without a consciousness, and for "mutants" to exist, who have different mental responses to stimuli than most people. Because he believes that both of these conclusions are ridiculous, he rules out substance dualism.
However, I don't see how the idea that the mind is not contained inside of the brain necessarily makes either of those options possible. As to the zombie theory, just because the two components of mind and body lie in different realms, it doesn't seem to make it necessarily true that the body would be able to function without the mind. The two could be separate but still rely upon each other in order to function.
For the mutant idea, I don't see how that would be any less possible if the mind occupied the brain, all it requires is that some peoples' brains be wired differently; the separation of the two does not seem necessary at all for this to be possible, and thereby it seems totally irrelevant to this discussion.
Thus far I've had no problem with the book and while it could be a simple matter of us disagreeing on the topic, I feel like I may be missing some part of his argument that would make his conclusions clear to me. Any help elucidating this argument would be much appreciated.