It is annoying to be asked about smoking as though you deserved the cancer. I wasn't content with just a no but went on to explain that my mom smoked a pack a day from the time she was 14 until she quit at 70. Not a trace of lung cancer or oral cancer even though she also drank "high balls" daily. Oh and her diet was terrible and when she quit eating out of grief when my dad died of a heart attach - it was the beginning of the end. Her father drank and smoked really heavily right up until he died of liver problems - again zero cancer.
I agree that it seems to be a way for people to reassure themselves that they won't get cancer because somehow I had to be at fault. Although recent studies on HPV and its interaction with gum disease may very well prove (apologies to Jimmy Buffet) "Some people say that there's a (insert cancer cause here)to blame, now I think, hell it could be my fault"