I don't doubt you, but that's not a rigorous method to assert a hypothesis, what about VonMessa's story? There's your proof by contradiction to your 'for all' assertion.
Ive seen accidents caused by people talking while driving. So why not pass a law outlawing "talking while driving", or, "scratching your bum while driving". When do things cross the thresh hold where Big Bro gets to step in and intrude even more in our lives? Stealing even more of our wealth? I for one refuse to write this ticket. Unless the driver doing it is so engrossed they arent paying attention to the road. And we already had a charge for that ; Its called "negligent driving".
As for "rigorous methods" those usually involves "statistics" which are a form of witch craft all their own. "We" dont have much respect for them so why should you?
I'm sure you know a lot Rich, just your delivery could use some work
My delivery is done with a purpose. Its not personal so dont take it so. Your first two were a bit edgy too but Im still smiling. See

At my University they have a driving simulator lab and they run experiments constantly with overloading a driver's attention and then monitoring his / her ability to assimilate and prioritize tasks. Just like SA in AH, every distraction contributes to a reduction. If you throw in a critical driving situation right at the point of a critical conversation normal people (as opposed to fighter pilots, even simulated ones rock) just aren't very good at sorting that out.
Yes Universitys are great for "simulating" and "statisticale'izin". But they aint real life and again when does it cross the thresh hold when a bunch of elected idiots can pass a law whose real purpose, tho they deny it, is to create new revenue streams for Big Bro? Now Im avoiding the "P" word here while trying to make my point about "intrusion into our lives".
Chatting to someone in the car is slightly different because they are present and can also observe the driving situation.
If the driver is chatting my friend we can assume the rider is chatting as well and is just as engrossed.
Even talking on a hands free set detracts although it's probably at the lower end of the list. You are right about the other mundane tasks people do, they shouldn't do those either and some of them are worse. Once I rode my motorcycle behind a car driver who was having a shave and putting on his tie etc at 70 m.p.h. on a dual carriage way
Ive given long, accurate, continuous radio comms while chasing a felon at speeds up to 120 mph for 20+ mins and without cracking up. I have no special powers that others dont have. 30+ years and Ive never cracked up a squad despite all the mayhem and many, many citizens have stellar driving records as well. Despite talking on a cell phone while driving, which BTW I also do.
My Gosh! We let deaf people drive, badly disabled people drive, people so dang old they think they are still in their '46 Buick, yet we calmly accept this nit wit law on cell phones. My friend the longer Im on this job the more Big Bro, and its vision of imposed Utopia, scares me. We cant talk politics here so I'll leave it at that. Next is stop sign cams and speed cams everywhere, to go along with real time cams all over the place. Eventually it will be robots, retina scans, and "Pre Crime".
Im just glad I remember a simpler time where people had individuality, honor, common sense, and responsibility.