Your first example is not comparable to an addiction. Its an entirely different situation and I am honestly not sure why you brought it up. This isn't a discussion about that.
There really are no more angles to an addiction. The only changing factors would be how they began the addiction and if they want to break it or not. There is also not a legit reason to smoke a cigarette. Now, if you are speaking of weed, I wouldn't care. He needs it for medical purposes. I would not think twice of allowing him to smoke so that he can take care of himself. Though I may inquire as to why he wouldn't prefer to do it at home.
You cannot help someone with an addiction. Change must come from them. The only way one can help is by offering them the solution and tools to get clean when they are ready to do so. It may be in the form of keeping them from purchasing any more, or stopping them whenever you see them smoking. However, you cannot do it for them. This is where you produce a fallacy in your argument. You don't take in a smoker to cure them as you would take in someone who is sick and give them medicine.
Its also not a matter of opinion that they are disrupting peoples lives. Its a documented fact backed by medical research. 1,000 babies die a year from mothers who refuse to quit smoking while pregnant. Death is one of those things that is more then a "disruption". Its a permanent end.
On average, 46,000 people Die yearly from second hand smoke. I got that number from the 2,500,000 people who have died as a result since 1964.
This is why I simply do not understand smokers. They do not seem to care that they could kill someone as a result of their second hand smoke. I would say that I do not understand why its still legal, but, money.