I think the counterargument here is that if you don't need to move humans to work and back home again every day, and if you don't need to optimize workplace conditions for humans - by providing creature comforts and safety equipment - your unemployed human is using much less resources than a working human, and the robot is also using much less resources than a working human, so the sum of unemployed human + working robot may add up to less than working human alone.

That, and also resources are here to be burned for our comfort. We should, by all means, burn the minimum amount of resources required for said comfort. But still, there are here to be burned. Otherwise, to minimize resource usage, let's all give up on civilization and go back to caves.