The studies I have seen also say that driving while other people are in the car, and especially while eating, is also distracting. Driving is a balance of many things, spreading your attention to the gauges, the road, the mirrors, any pedestrian traffic, cross-traffic, road signs, as well as anyone in your vehicle, on the phone, your car radio, eating, or a number of other things.
Do you propose that the driver be completely isolated from all distractions? How about if he is tired? Should his car refuse to start if he had a bad night's sleep?
It has ben up til now, left to the judgement of the individual what they can handle safely. I'm not saying that the judgement of all people is sound; on the contrary I believe that most people aren't smart enough to be given a "forward" button on their e-mail, much less manage distractions in their car, plan for their own retirement, vote, or bear children. This still doesn't change the fact that I don't want my choices limited based on the bad judgements/stupidity of others.
