If literally all imaginable human work was 100% automated then the cost of goods and services compared to today would be tiny. The poorest member of that society would live like a king from our present day world.
If you had robots making everything you could possibly want, why would you bother selling any of it to people who don't have any land, natural resources, or rare skills? They wouldn't have anything you want.
The idea that you could do something like that is even more outlandish than having robots that could automate everything a human could.
But I didn't say this.
Certain materials can be substituted for another, but for high energy costs in making them.
Well, that assumption is pretty general and doesn't account for natural resources/raw materials, energy inputs required for production, or other factors. It would also vary per sector, such that the statement is far from universally true.
>The poorest member of that society would live like a king from our present day world
But, regardless, there would be some cost for goods. How do you propose the now 100% unemployed population pay for anything, let alone "live like kings"?
The answer is that you would need to devise a method of wealth distribution that is orthogonal to capitalism. Say, for instance, a tax that subsidizes everyone else. That, of course, would not be capitalism.
The point is that wage labor is fundamental to capitalism. Somewhere between our present state and 100% automation, a capitalist system requires so much intervention that it breaks down.
You forget things such as: meaningful work, respect from society, crime, cultural differences between the poor and the rich, interclass upward mobility (see any sociology textbook), intellectual stimulation.