Biology is very complecated, and human is even more complicated! Please do not be emotional, it dose not help!
I did eight years research in inbred mouse models(like identical twins), when you give them the same diet, some of them develop certain disease, and some do not. So, in biology, no diease is caused by a single fact, but rather multiple causes. That is why you see non-smokers get lung cancer.
Smoking or non-somking is a personal choice, but smoking is definitely a bad choice. As a physician, I advise people do not smoke and quit smoking.
