> unless you increase the population.
That doesn't help either. If you are increasing population without that population having wealth (and generally the wealthier you are the fewer kids you have) you dilute the distributed wealth of the poor to the point where they no longer have the economic influence to warrant hiring shelf stockers or burger flippers because they have no money.
> There are already a number of prototype burger making robots, for instance.
The automation of service is not coming in the form of robots doing a service workers job, its computers obsoleting the service. It is the same thing trying to make the "perfect" veggie burger vs learning to love naturally vegan dishes.
It is companies like Amazon that are displacing service workers by the thousands. There is so much potential revenue to be made and costs to be saved by having a wholly automated supply chain, and eventually you are having your burgers air dropped on demand by drone rather than having to go anywhere in a self driving taxi to get the burger. The logistics of service will... are... changing fundamentally, constantly, every day, progressing towards those eventualities.
It is not a problem tax rates or "American grit" solve. It requires a rethinking of your economic system when you finally accept reality that swathes of productive gains are not being made by the sweat of a single human being, at which point the fruits of those labors are no longer compatible with traditional laissez faire capitalism.