> If you're using the autopilot to provide smoother control, and as a second set of eyes on the road, then thinking it's on when it's off isn't of much consequence

I understand the sentiment behind this statement, but I'm not sure I agree.

Compare with simple cruise control -- ordinarily, the driver needs to provide constant gas pedal input to overcome inertia at highway speeds. If for a moment the driver thinks that cruise control is on but it's actually off, the car will begin to appreciably coast, making it clear that it's off. The 'failure mode' of this scenario is rarely surprising or dangerous to the driver or others, and easy to recover from.

Whereas features like automatic lanekeeping, blind-spot warning, pre-collision emergency breaking... those are features that need to work unless explicitly disabled, because the failure modes all end in a potential accident.