> 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)

I think you're right that a lot of people would like to believe this, and that attempts to do so can't work because the idea is incoherent.

> My personal experience is that consciousness, like free will, is a useful illusion.

I would answer this another way, though. I would say that, for example, Amazon is conscious, and its consciousness is Jeff Bezos. The relationship between Jeff Bezos and Amazon is precisely identical to the relationship between your "consciousness" and you. But that relationship is not an illusion; it does exist.