I think I have the answer why people begin smoking, well I do have several theories atleast to be backed by my own experience (not smoking though).
1. They begin smoking simply because their friends are, and thus it's "cool" to smoke.
2. Group pressure. When I was in school I was encouraged to smoke by my friends, and was considered not to be as cool as they were. I have always had a will of my own, and no one has ever been able to force me into something, nor try anything I think is wrong. In my brother I see a totally diffrent personaliy, and he has fallen victim to group pressure and have tried both alcoholic (nothing seriously wrong here though), tobacco (cigarettes) and some other stuff I prefer not reveal to you due to the sensitive matter. He has a weaker personality and psyhic than I do, and is a text book example of a person falling victim to group pressure.
3. Parents forbid their kids to smoke, thus encouraging them into to doing something that is "forbidden", and by doing so they think they are cool alternativly rebellious for going against their parents. (Comeon we all know we liked doing stuff our parents said no to

)
4. Commercial (not sure about this one though). I am sure some people are influenced by commercials from tobacco companies, and this was true in the past that people begun smoking after watching commercials. Today I don't know about it, other than tobacco and alcoholic commercials are forbidden in Sweden.
5. The tobacco industries have far superior economic means to spread their word than those that work against them, that opposes smoking. This will lead to the success of my 4th possible theory.
6. Some may have tried because they were curious about this thing called "cigarettes".
7. People in development countries are a prime target for the tobacco industry, since there are no one around that knows the risks involved in lighting that cigarette and inhaling the poison.
8. Poeple still live in the past believing "smoking is not bad for your health."
.......perhaps r smokers just the lowest form of subamoebic lifeform that can be possible............
I wouldn't go as far as to call people stupid simply because they smoke. I may go as far as to admit smoking is stupid, but not the persons themself. I know quite a few "smart" people that smoke, and they at times wish they didn't, but it's hard to quit.
Such a comment I would never say. I am glad I didn't start smoking, but I can't really blame or look down at those who do, cause there are so many factors involved in one starting to smoke. Add to this the fact that there are substances in the cigarettes they add that adds to the addiction and makes it a pain in the ass to quit. (Yes, other substances than nicotin).
If this wasn't the case, why would the tobacco companies refuse to release the full composition of a cigarette, with all substances in them? The answer, they don't want to admit / show they are adding stuff that adds to addiction.
So to sum it all up:Yes, smoking is stupid
No, the people smoking are not necessarily stupid.
Some were "forced" into smoking.