I think hands free (including bluetooth) is no worse than having other people in the car talking to you really...and i think it should be a non-hands free talking/texting ban not a complete cell phone use ban since smartphones have essentially replaced gps navigation devices and mp3 players...
Actually, the statistics show that when you actually have a passenger, you are less likely to end up in a wreck. However, simply talking to someone on the phone, you are more likely to end up in a wreck.
You are right to a point...but I can argue so can listening to music and driving. Yeah I think long conversations should be avoided. If its more than "You need me to pick up what... ok bye" .. , "I am driving is it an emergency", or "Dont for get to pick up ______ from _____ its already 5 mins until (activity) is over".
So yes there are times when you need to talk and drive and it can be done with out the need to pull over. Now if you need to do a business deal or something drawn out then I agree pull over or tell the person you will call them back.
There is really no way to make rules and regulations based on how long or in-depth your phone conversation can be.