Yeah, I've heard all those excuses galore. "I prefer to die 10 years younger but live happily", or "the doctor says I have the heart of a 20-year-old", etc. Well, all those sportspeople who suddenly die at 20, also had the heart of a 20-year-old. Not everything can be seen with a basic checkup.
Plato stated that no person knowingly does evil, and I tend to agree. I think, at some deep level, smokers really do not understand that smoking is harmful.