Earlier this year, I watched a video that caught me entirely by surprise: A clip from the CCTV Spring Festival in China, in which more than a dozen humanoid robots performed an intricate martial-arts routine. They backflipped. They high-kicked. They wielded swords and dropped into potentially pant-splitting lunges. A side-by-side comparison with their movements just the year before was astounding: The robots, made by the company Unitree Robotics, could now move with a fluidity that looked less like the archetypical “robot dance” and more like ballet, albeit a dead-eyed version.I was impressed, but—I must admit—a part of me felt threatened....