It means that consciousness nothing special/supernatural. There is no soul, there is nothing but chemical reactions that manage to create something that is able to claim "I think therefore I am"
The illusion is the fact that we claim that we are able to "experience", but I think that its all just layers of GOTO reactions that create something that think its special. Much like how a program isn't considered conscious, but its very likely its because we haven't dug deeply enough into the layers of shit that is required to make a self-aware computer
We as a species may lack the mental faculties to truly understand the mechanisms by which life evolved the ability to analyze and reason about its surroundings and itself.
We lack the scientific tools to properly differentiate or falsify "consciousness" from any other sufficiently complex phenomenon. We can't tell whether it's an emergent phenomenon arising out of a particular arrangement of energy and matter, or whether it requires some input that we cannot currently observe/measure, or something else entirely. We don't know whether we can create consciousness from its constituent parts, or if it even has constituent parts. We don't know if there's a finite supply of it in the universe, we don't know if it's a dimensional thing, we don't know how it interacts with other forces.
We do know that it appears as though we have much more agency than a rock, yes, but it's a matter of degree how much more when we compare ourselves to other lifeforms, primates, dolphins, elephants, ravens... or other people. We don't know if certain members of our species are "more" or "less" conscious. We don't fully know what happens to consciousness during comas or brain death or dream states or sleep.
It's just an ambiguous term that we apply to the "state of human information processing that we can't really explain". Substitute "ambiguous" for "illusion" if you prefer, but it could also very well be an illusion the same way centrifugal force is a pseudo-force, i.e. the measurement of consciousness depends on some reference frame that we don't know how to use yet.
It's entirely possible that consciousness is NOT an illusion, that it is indeed a special "thing" in the universe, but we can't prove that with the science, language, philosophy, and possibly mental capacity that we currently have. Maybe one day we will. Maybe not. But it's premature to assume we understand anything about consciousness in the philosophical sense.
Why are you concentrating on individual animals, where herd behaviour of them can not be explained by behavior of individual. Same applies to people - there are enough of examples in history of groups of people believing in God and his plan and that belief has led to catastrophic consequences for tribes and even nations...
For all I know nothing really matters - Sun can go Nova or Earth can be hit by a small planet and Life on earth can go extinct.
I don't understand what you're trying to point out. That groups of things can have behaviors that lone individuals don't exhibit? Yes, that is true, whether at the atomic level or the cellular level or the family level or the population level or the species level or the ecosystem level... it's very fascinating, to be sure, but in what way does that prove or disprove any sort of god? It's just the same Watchmaker argument, i.e. that complexity requires a maker, which it arguably does not. Complex behaviors, even flock behaviors, can evolve from the sum of its constituent parts. A pinball machine with eight balls in play will react very different from one with a single ball or no balls, but nobody accuses the pinball machine of being sentient (or if they did, I'd really like to play that machine).
> For all I know nothing really matters - Sun can go Nova or Earth can be hit by a small planet and Life on earth can go extinct.
Yes, and? I wouldn't worry about it too much... you'll likely die from something far more banal, like plain old climate-change-driven political instability, North Korea, the next anti-vax movement, etc.
