> It's an unconfirmed and probably foolhardy assumption that the brain alone creates and supports the existence or propagation of consciousness.

This is not an assumption that science makes. However, we have never observed consciousness in anything that does not have a brain, and physically altering a brain can cause fundamental changes in consciousness. So, until there is evidence that consciousness is not tied directly to a brain, its the best working model we have. Suppositions to the contrary are interesting but meaningless without being supported by evidence.