Quite. The vast majority of of collisions to date have been human error. Specifically, rear-ending on motorway on-ramps. The driverless car is obeying the rules. The human driving the car behind devices to take a chance in the merge...Until, of course, someone hits one that was doing something dumb - like obeying highway code of traffic womble signs left on since last week...
And the huge weakness is insurance against coding errors that can't deal with foggy day on M25 and some human muppet who can neither defrost their screen, use indicators or turn lights on
A variety of systems, not just vision, will be used. Lidar, for instance. Fog won’t be an issue. As you say, humans will.
But that’s not the fault of the technology.