The answer is the person behind the wheel.
Tesla makes it very clear to the driver they you still have to pay attention and be ready to take over any time. Full self driving engages the in cabin nanny cam to enforce that you pay attention, above and beyond the frequent reminders to apply turning force to the steering wheel.
Now, once Tesla goes Mercedes and says you don't have to pay attention, it's gonna be the company that should step in. I know that's a big old SHOULD, but right now that's not the situation anyway.