If you create a system that by design will cause the driver to lose focus, you are responsible for the driver losing focus.

Saying “we told the users that they must pay attention while they are not driving”, or “we told them that the system called ‘auto-pilot’ is not actually able to autopilot the car”, and “we advertised the car’s self driving ability but had documentation saying it doesn’t actually have that ability” then you are responsible for that system driver behaving exactly as you would predict.

Their have been numerous studies that show that people stop paying attention when they are given menial or non-focus dependent tasks. Saying that the only safe way to use autopilot is by not being a human is fundamentally the same as saying “the brakes in the car only work if you press them continuously for 5s or apply 300lbs of force”.