I think people start with the premise that consciousness is a specific “thing”, that it is unique and special to humans (and maybe dogs because we like them but definitely not spiders and flies because we don’t) and then try to work backwards to define it in some ways that keeps it special. I don’t think consciousness is so specific, and I think people aren’t clear about how they think about it as something separate…
"Consciousness is an illusion" I take the word "illusion" to mean, some type of experience which misleads one about reality. And "consciousness" to mean, the experience of having experiences. So I parse this claim as something like, "People both do not have conscious experiences, and also do continuously have a particular type of conscious experience: a misleading experience which leads them to believe they have cons…
It's not that consciousness is illusory. Rather, consciousness is synthesis.
A synthesis of sensory inputs as interpreted by multiple, sometimes competing, semi-independent systems combined with stored patterns based on previous subjective "experience", creating a narrative about you and the world.
That narrative is our subjective experience, our "consciousness."