That's a reasonable argument. In that case, I argue that the manufacturer who wrote and signed the firmware should be liable as the operator of the vehicle.
Do you think it would be possible (and desirable) to split liability, or should it remain solely the manufacturer's?
If the regulators step in to remove the vehicles from the road then who makes the consumers whole now that their vehicle, and perhaps livelihood, is gone?
I suspect certification is the only reasonable path. If the regulators believe these systems are safe for the road then they should build the framework for establishing that bar. If such a framework is not possible to build then I think that also answers that question.