As a former smoker, I think this is a good idea.
Smoking costs the public enormous costs in terms of healthcare.
Like hundreds of thousands of extra per liftime. That the NHS has to pay.
Here’s a study from 1990, add inflation and such https://www.nejm.org/doi/full/10.1056/NEJM199710093371506
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.