In the US, there is a legally mandated freedom of religion. In other countries, they outlaw certain religions. I would not want the government to tell me when, where, if, etc. I can be Morman. I believe in freedom of religion.
My problem isn't with the smoking (heck, I used to be a smoker), it is the fact that he was doing it in the car with the kids and exposing them to second hand smoke which has been proven to be dangerous. US laws that appear to restrict liberty are created with the underlying intent/excuse of protecting the health, safety, and welfare of the citizens. In this case, the children cannot protect themselves so I think it is appropriate for the government to step in and offer protection. A lot of cities have outlawed smoking in restaurants and this would be in the same vein, but also focused on protecting those who can't protect themselves.