I'm not suggesting that what you are saying about hands-free use is not true, although I haven't seen any statistics about what proportion of accidents hand-free phone use is determined as the cause compared with the many causes of RTAs. 

Since conversations apparently are a cognitive distraction, then I would imagine that conversations with a passenger, kids in the back etc. would also produce the same distraction; even more so for those really scary drivers who look at their passengers while talking to them.  

Also perhaps even listening to a radio play - maybe some people's minds wander.   Some people don't concentrate enough when they are doing none of these things.

I wonder what proportion of accidents are caused by drivers talking in a car.  Not that we would ever know.

I suppose my point is that yes, we need to do what we can to lessen road traffic accidents, but laws need to be made in proportion to the risks.  Until I see evidence for myself that hands-free phone use is more dangerous than talking or listening to the radio, or using a sat nav, I'm not convinced that hands-free needs to be banned.  I imagine that for some people the technology is very helpful in their work

Just my opinion, I don't use a phone in my car, I don't have a hands-free kit, and I don't use a sat nav.

All might be irrelevant if and when we have driverless cars, but I expect they will throw up some problems.