Why spend time and resources in activities you know significantly damage your health? Doing so steals the most valuable possession possible - years of healthy life that might have let you reach an age of radical life extension - from the person you will one day be. You're picking your own pocket, cutting your future self short. For example: "The smoke of cigarettes represents an important accelerator of the aging process, both directly through complex mechanisms mediated prevalently by excessive formation of free radicals, and indirectly by favoring the appearance of various pathologies ... smoke compromises not only life expectancy, but also the quality of the life, favoring the occurrence of non-autosufficiency. Smoking is an important risk factor for many diseases, such as cancer, cardiovascular and respiratory diseases. ... Non-smokers have a much higher life expectancy than smokers, and the suspension of smoking is accompanied, even in the elderly, by an increase in the survival time due to the reduction of smoke-induced biological damage. ... Among [centenarians], smoking is extremely rare, and even when it occurs among them, it is correlated almost exclusively to bad health conditions and non-autosufficiency, indicating that it compromises health status and the quality of life even in extremely long living subjects."

Link: http://www.ncbi.nlm.nih.gov/pubmed/17686596