Your tax dollars go to many worthless ventures of government and also medical costs. You pay to save drug-users and criminals, welfare mothers and new children, drunk-drivers who get in accidents, etc.
Also, your "fact" that the cost of cigarette taxes does not cover the cost of Medicare spent on these individuals has been shown to be false. Smokers tend to die earlier, for various health reasons, and thus forfeit Social Security benefits that non-smokers utilize, due to their longer life spans. Also, non-smokers will utilize Medicare benefits longer than smokers.
Also, why did you use the idea of lung cancer killing more people than AIDS and Bovine Spongiform Encephalopathy? AIDS still kills predominately gay males (in the US) which is a small population compared to smokers, and BSE is such a rare disease it is nearly irrelevant.