The zombie trail is a well-trodden path, so I thought I might venture out myself:
The logical possibility of a zombie world -in which humans behave identically to the way they do in the real world but in which conscious experience is absent- is often used in antiphysicalist arguments to show that consciousness does not supervene on or is not entailed by the physical facts of the world.
However, another consequence of the zombie argument is that experience is relegated to an inactive, epiphenomenonal role. So while the zombie argument may provide some foundation for panexperientialism, this is usually at the expense of any causal role for experience.
The standard zombie argument goes something like this:
1. Human behaviour is determined by purely physical laws (this premise may not always be explicitly stated).
2. In a zombie world the physical facts and laws are identical to that of the real world.
3. Therefore,in a zombie world human behaviour would be the same as it is in the real world.
4. Therefore, a zombie world is logically possible.
However, an equally valid argument is:
1. Human behaviour is only explicable as being enacted by a conscious, purposeful agent.
2. In a zombie world, conscious purposeful agents do not exist.
3. Therefore, in a zombie world humans would not act the same way that they do in the real world.
4. Therefore, a zombie world is not logically possible.
In both cases the reasoning is circular and the only significant premise is the first one. I think the zombie question only really becomes interesting when it is addressed from a standpoint of empirical investigation and metaphysical reasoning, rather than merely by appeals to logic and language.
In most zombie discussions, the premise that human behaviour is determined by physical laws is simply assumed without much elaboration. However, I do not think the truth of this premise is at all settled.
For instance, physicist Henry Stapp argues persuasively that the deterministic view of human behaviour is based on a redundant, outmoded classical physics that is not applicable to all activities of the functioning brain. Stapp contends that indeterminacy at the quantum level allows for consciousness to affect bodily actions. For a layman’s guide to the interaction between consciousness and quantum physics I recommend his book ‘The Mindful Universe’, available for download at his website here.
A similar point could be made regarding the distinction (originally proposed by David Chalmers) between the ‘hard’ and the ‘easy’ problems of consciousness. The easy problems of consciousness are those which supposedly are in principle solvable by neuroscience (e.g. how the brain processes environmental stimuli, integrates information and reports on internal states), whilst the hard problem relates to the fact of phenomenal experience itself.
However, this dichotomy tends to automatically assert all behaviour as being explicable in deterministic terms and again relegates experience to the position of epiphenomenal bystander.
It may be the case that many of the so-called easy problems - in particular, those concerned with the influence of conscious purposes on behaviour - may be inextricably bound up with the ‘hard’ problem.