If a point has been missed then I reckon that lies squarely with your assumptions. For one thing smoking does harm the health of both smokers and passive smokers hence the need to regulate. You are right to point out that anything in excess may result in health problems but in such instances the emphasis would be on helping people to understand the need for a balanced diet not to stop them consuming alcohol, chocolate, red meat etc altogether. Those responsible for selling the latter items are only interested in selling more so someone has to intervene but in a balanced way only. 

Smoking is nowproven to be both addictive and a health hazard, making it more difficult to be seduced by the weed and easier to quit would seem a perfectly responsible approach whilst ultimately leaving the final choice to the individual.