>"Autopilots do a lot more than that because flying an aircraft safely is a lot more complicated than turning a steering wheel left and right and accelerating or breaking."

Can you elaborate? My very limited knowledge but of very real airplane autopilots in little Cessna and Pipers is that they are in fact far easier than cars - they are a simple control feedback loop that maintains altitude and heading, that's it. You can crash into ground, mountain, or other traffic quite cheerfully. I would not be surprised to find adaptive cruise in cars is far more complex of a system than basic aircraft "autopilot".