Easy to answer.
I have known a number of people who would be considered obese. I have seen their valiant efforts at diet and exercize and yet, as one of them put it "I drink a glass of water and I gain 5 pouns". In short, there are many obese people who are not obese because of irresponsible choices but because of metabolic and genetic hereditary issues. To punish anyone for something that is not a complete choice, is as morally wrong as I can imagine. Myself, I am anything ut obese, I'm what you would call slender.
Tobacco is a completely different choice. True, it is highly addictive and for some, at least, very difficult to quit. But it isn't impossible to quit. I am a smoker and I would still advocate for eliminating all formal, legal options to continue my habit with. If I just can't quit, then I must choose to take the risk of growing and curing my own tobacco, in secret and in shame. Since I have a "black thumb", I assure you I would just quit. But it certainly has been my CHOICE to continue.