Well we know that it exists, or at the very least seem to exists. And there is nothing in the physical word that we have understood so far that cannot be ultimatly expressed computationally—even if it’s usually not the most useful formalism. It is of course somewhat a leap of faith to then say _everything_ is computation (or can be expressed as computation), but I would argue that science has already made this leap in it’s infancy: The Book of Nature is written in the language of mathematics… Admittedly, modern philosophy of science is a bit more nuanced but the old the statement from Galileo basically stands. Now I agree that it’s not entirely rational, but it certainly isn’t “religious”.
So yeah, I think there are very good arguments to be made that conciousness can at least in principle emerge from some kind of computation. That computation could be a complete simulation of every atom in a brain or maybe some shortcut is possible it doesn’t matter for my point. That does not mean however that I think it can be made or will be made, since has you pointed out, we have no idea what we are talking about. I completely agree with Lanier in this, the tech industry should stop focusing on this nonsense.