You draw the line proportionally to how dangerous it is. The government regulation dangerous decisions is nothing new.
They put fences around cliffs. They ban driving under drug influence. They regulate driving with driving licenses. They force cars sold to meet certain safety standards. They regulate the max radiation that devices are allowed to output. They tax certain foods more than others (such as sugar-heavy foods). They ban certain construction materials (asbestos, lead).
The list is almost endless.
If you want personal vices, sure.
Max sound volume (some people enjoy listening to really loud music). Max road speed (some people enjoy going really fast). Casinos (some people enjoy gambling). Animal fighting (some people enjoy watching those).
Each of those for a variety of reasons
- Annoyance of others (which could lead to severe health effects)
- Safety of others
- Your own wellbeing
- Animal rights
I don’t see why smoking is this special that can’t be regulated. It was regulated already.