What about passenger conversations?
They are not. Here's why.
On average, having a passenger in the vehicle actually makes the driver safer than if they were driving by themselves. The reason passenger conversations are not as dangerous is that passengers act as another set of eyes, adjusting their conversation as driving becomes more difficult and pointing out hazards and helping to navigate. Of course teens and and small children don't modulate their conversation as a function of driving difficulty (which is one reason for the laws that restrict the activity of teen drivers as they learn to drive).