As a general principal, I would disagree with the position that it's not valid. Certainly some people who quit smoking late in life prolong a painful cancerous demise, however I would imaging the worst of the low-quality disabled years are often a result of the limited, desperate nature of the available potential life-saving treatments: radiation/chemotherapy, etc. A significant percentage of smokers quit late in life and avoid those extremely low-quality disabled life years. Also, it seems perspective typically changes as 'quality of life' decreases, generally resulting in the desire for continued respiration;-)
