Believe it or not, if robots can perform heart surgery on human beings, they can harvest crops. Several companies in California have been working on robotic harvesters and other mechanical harvesters, but the powerful United Farmworkers Union has thwarted forward progress on this.
Reckun they can teach them robots to cook, clean, paint, construct buildings, dig ditches, mow yards?(oh wait, they do have robots that mow yards) I don't know what the availability Of legal potiential employees there are out there but, I bet it's not 10 to 20 million people.