The obvious counterargument is; no matter how much better our simulations of fluid dynamics in water get, they never get any wetter. "Wetness", it seems, is a property of reality that can't be digitally simulated.
Similarly, no matter how perfect your simulation of cognition, there's no reason to think it will ever be conscious. At best, you're creating high-resolution digital ghosts. Which may freak out the living, but do nothing whatsoever to extend the life of the person simulated.
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