Great point. It's safer to fall asleep at the wheel of an autopiloted car vs. one than one that isn't.
In the early days of seat belts resistance to them was strong, with specious arguments in the same vein as some above. Same with air bags, "They'll encourage reckless driving."
One day there'll be no steering wheels or controls taking up the valuable space needed for our naps and snoozes. 
Seatbelts or airbags may reduce injuries or save lives, but one would still have the burden of repairing their car if they should crash it. That's a significant financial incentive to continue to drive safely even with belts and bags. What incentive is there for people not tune out and let semi-automated systems take over? There have already been numerous documented crashes where the driver "thought the auto emergency braking" would stop the car for them so they put their attention on texting their friends.
These semi-autonomous aids need a consequence to encourage people to stay alert. Like if the emergency automated braking kicks in more than once inside of 30 minutes, the car starts squawking at you or goes into a limp mode that cuts top speed and disables most features.
