"Do you believe that cigarette smoking causes lung cancer? Yes or no?"
No. It may increase the risk factors of contracting lung cancers, or other diseases, but it is not a causal factor. Genetics is far more influential in contracting lung/heart disease.
Now, how about offering your answer to my question. Why is the highest per capita population in the world, Japan, also the lowest per capita heart and lung disease incidence in the world?
Then you should inform the World Health Organization, the Centers for Disease Control and Prevention, the US National Cancer Institute, the office of the US Surgeon General, as well as RJR, Philip Morris, and all the other tobacco companies, all of which agree that smoking causes cancer.
While you are technically correct that smoking increases the risk factor for lung cancer, you'd be equally correct in saying that pulling the trigger of a loaded gun aimed at your head increases the likelihood that you'll be shot in the head.
Regarding Japan, it's likely genetics and diet may play a role on a population level. However, Japanese smokers are far, far liklier than Japanese nonsmokers to develop lung cancer, and Japanese lung cancer rates have skyrocketed over the last 100 years, tracking remarkably the increase in tobacco use. If you'd like more information on cancer statistics in Japan, I'd be more than happy to refer you to relevent studies.