Consciousness is unique in that we, as yet, have not identified any externally observable properties that could not also occur in the absence of consciousness. This is not true with matter.
Normally when we debate what something is, what we are actually debating about is what it does, with the implicit assumption that the "is-ness" of a thing is defined as the complete collection of all the properties it exhibits.
As it does not seem possible to do this with consciousness, it is not possible to debate it. It is conceivable that this implies that consciousness cannot exist, but that depends on your metaphysics.
Normally when we debate what something is, what we are actually debating about is what it does, with the implicit assumption that the "is-ness" of a thing is defined as the complete collection of all the properties it exhibits.
As it does not seem possible to do this with consciousness, it is not possible to debate it. It is conceivable that this implies that consciousness cannot exist, but that depends on your metaphysics.