China has become the world's second-largest economy by manufacturing products faster and more cheaply than other countries. Now, China's massive factory workforce is being replaced by robots, and many people may be left behind. In the US and other developed countries, fast-food workers, office staffs and sales personnel also may soon be shouldered aside. And robots are teaching classes, researching legal cases — even writing news stories — without demanding vacations or time off. As robots become more creative, will guaranteed incomes be needed to sustain an unemployed middle class?