I've worked on highly safety related (classification ASIL D) automotive systems. There are rules about how to think about the driver.

The driver is not considered a reliable component of such a system, and must not be used to guide decisions.

Yes, the driver clearly was a fool, but system design should not have taken his decision into account, and come to its own conclusion for a safe reaction (e.g., stopping the car).

I agree with that, and as I say I'm not attempting to defend Tesla in the slightest.

My point was simply that the driver has to take responsibility for their actions in this situation as well.

If the robocar were to warn once, and then steadily slow, all drivers would learn to take over when warned.

I don't disagree - like I say, none of my comment was intended to let Tesla off the hook in any way.

My point was simply that the drivers who use semi-automatic cars and choose to ignore warnings to retake control need to be responsible for their actions as well.

Incapacitated? The software needs to fail more gracefully than this when the driver is a dependency and isn't responding.