>How can you have any definition of consciousness that says humans do not possess it,

I'm not obligated to prove the negative.

>Isn't consciousness phenomenon that's literally derived from human experience?

You grew up watching and seeing all the various illusions caused by how your brain works/malfunctions, but this is the one experience you're sure is the real deal? The one telling you that it's a scientific fact that you have a woo-woo spirit in your skull, and that neuroscientists are going to find it any day now?