A counterargument might be that consciousness is an inherent side effect of all the stuff that goes on in the brain. And while yes, the brain does some computation, that is by no means a complete description of all the brain does and is. So computation of any sort will not necessarily produce the side effect if you just do enough of it. Rather it's a side effect of the way the brain works, which is not the way a barrel full of pocket calculators, or a Macbook, or a bunch of rocks in the sand works.