I think outlawing it so that 90% follow that rule which then decreases the overall activity. Murder is banned. It still happens but (somewhat) less than if it were not prohibited ... Most people decide for themselves that murder is not worth it ...
In principle, I totally agree that smoking/vaping is bad. Lungs were designed to breath air - nothing more, nothing less. Anything else is harmful to them.
Smokers/vapers have proven that they can choose their time/location so should be able not to indulge inside a car just as they can currently wait until they're outside a building.
BUT
Having spent a lot of time with teens, how can this possibly be enforced for the coming teens? Even the current restriction '18+ only' is impossible to enforce.
(Alcohol/bad food is a personal choice and does not affect the immediate vicinity: if someone is drinking, it does not make me drunk but if someone is smoking/vaping, I have to breathe that too, especially in an enclosed space.)