People claim smoking cigarettes is a choice. Unfortunately, it is not a choice for those who are forced to come into contact with the deadly particles that come as a result of smoking. You may state that people can simply avoid the smokers, but it is not that simple. Cigarette smoke lingers for hours to days on materials. Individuals who have asthma can have serious reactions when indirectly exposed to smoke even after the smoker has left. By reducing the ability of minors to purchase cigarettes, less people will be addicted to these drugs in the future.
Here in America, we had the 18th Amendment that illegalized the use and sale of alcoholic beverages during the 1920's. The effect was an increase in organized crime because one could only get alcohol by illegal means. This put vast amounts of money into the hands of criminals like Al Capone, allowing them to rule the streets unchecked. To illegalize cigarettes in any way would elicit a similar outcome. Organized crime rates would increase, as gangs would be making massive profits, allowing them to purchase greater means of violence and control in the streets.
Aside from the serious and likely violent black market this would create your body should belong to you, not to the government. Arguments used to make your body government property often appeal to financial issues of lifestyle choices but then some studies suggest cigarette smoking actually saves taxpayer dollars by cutting out old age health expenses when people die early. Regardless of which studies are right as pertains to cigarettes if you wanted to be consistent in regulating personal behavior based on incidental effects on the economy then you'd have to have some laws requiring unhealthy behavior. That nobody is calling for such laws shows that the "it costs taxpayer money" argument is a pernicious cover for self-righteous moralizing.
Life is supposed to life. It's not supposed to be regimented down to every detail yet that's where this sort of thinking leads to. "Health" is NOT morality. Health is a consideration that various people make in their lives alongside other considerations. No consideration is superior to any other consideration within the context of one's personal life.
One might make the argument that they're not making a free choice because of addiction but the same argument could be applied to every human decision because all decisions are based on neurology. Thus this argument could easily be adapted into an argument for totalitarianism. But it can also be easily defeated. People's preferences for how they want others to behave and how they want others to think are also juts based on their neurology. Maybe we should cure people of wanting to persecute others for their personal consumption choices?
Everyone wants freedom in their personal lives by definition people want to do what they want to do. As long as it doesn't interfere with other people's lives they should be allowed to do that. It's that simple. I'm not arguing for full libertarianism as I do see a role of the government in resource redistribution. A person who starves or can't afford health care and dies is clearly not free. But your personal lifestyle choices should be entirely up to you, particularly your authority over your own body.
Nothing is more personal, nothing belongs to a person more than their own body.
To stop people from smoking. It has been a choice up until now and would only seem fair to remain a choice. Of course, educate the public about the dangers, knowledge is good, but to physically and legally 'stop' people from smoking takes away a right that is theirs. Sugar consumption is also bad for you, so IF smoking were to be legally and physically stopped in any way, I think it would only be fair to do the same with sugar. But of course, that's not realistic.