if some human does something wrong, it's possible to prosecute and penalize said human... if a swarm of drones did something wrong, who will you prosecute?
it's the same as the outrageous programming errors that go unpunished because "there's no way to know this piece of code would fail this way"
easy example: how many tech vendors got punished by using a hard-coded password that leaked? how many "vendor-supplied backdoor" leaked?
it's the same with autopilot: if the autopilot kills someone, the vendor won't be responsible (it wasn't us driving) and the car owner will say the same