if cell phones are mostly the cause and the gateway

Oh they are a serious cause, much as talking to passengers is. It is all a matter of degree. But you don't need to visualise a passenger.

I have seen videos of crashes where the driver was fiddling with a cassette. If it takes yer visual cortex it is that much more of an accident waiting to happen.

You wait till driverless cars go mainstream. Drivers will force the autoauto to give way, suddenly. The computer on the lap will be on the floor, while the driver will speed away oblivious. And it won't always be a driver, I can foresee kids playing chicken with driverless cars, until, one time, it isn't a driverless car, brainless maybe on their phone! And who do you blame then?