I wrestle with this one and am afraid that at the point a car is driving itself, a EULA that the driver agrees to which states: "I will always maintain concentration and control of the vehicle in the case things go wrong" isn't accounting for how the human brain actually works. Humans only make for good backup systems when they are engaged and/or have time to react. I'll give Elon some credit. This is one heck of an experiment with a life critical system.