[dragonwriter]

> An economy must consist of more than just knowledge workers. If a guy who's stuck stocking shelves in a supermarket gets an education and moves up to a career working at a keyboard, those supermarket shelves still need to be stocked.

Sure, but if the reason he stopped working as a supermarket shelf-stocker and got an education to move up is that shelf-stockers were in decreasing demand because of shelf-stocking robots or because of workers displaced from other non-intellectual labor because of robots, the shelves are going to be stocked, and he isn't needed to do that.