Everyone needs end of life care, the fact that end of life care is expensive does not mean that obese people or smokers don't cost more annually throughout their life than those who are of normal weight or don't smoke.
Annual Costs (these are studies from different years, but should still give you a baseline understanding): Obesity - $147 billion annually Smoking $170 billion annually End of life - $221 billion annually
That's end of life care of the entire population versus annual care of the 39% of Americans who are obese and 15% who are current smokers. I can't find numbers for the total number of living former smokers.
I'd rather pay the $935 million dollars annually that sports injuries cost (https://www.usatoday.com/story/news/nation/2013/08/06/injuries-athletes-kids-sports/2612429/) if it means that it is starting kids on a track to a healthier lifestyle. Also anecdotally, since that seems to be the name of the game around here, as a rising fourth year medical student, I see significantly more patients admitted to the hospital that fit into the former smoker and/or obese category than the "sports injury" category.
There are certain choices that more significantly impact the chance you'll end up in the hospital than others. This isn't blindly pointing at one of those choices and saying, "hey, we should tax them." There's a real financial cost to tobacco and added sugar/processed foods/whatever you think makes people obese (please don't say genetics), and I don't think it's unfair to put a tax on things that cause it to help offset that cost.
"The estimated annual medical cost of obesity in the U.S. was $147 billion in 2008 U.S. dollars; the medical costs for people who are obese were $1,429 higher than those of normal weight." https://www.cdc.gov/obesity/data/adult.html
"2010, 8.7% (95% CI=6.8%, 11.2%) of annual healthcare spending in the U.S. could be attributed to cigarette smoking, amounting to as much as $170 billion per year. More than 60% of the attributable spending was paid by public programs, including Medicare, other federally sponsored programs, or Medicaid." https://www.ncbi.nlm.nih.gov/pubmed/25498551
"approximately 13% of the $1.6 trillion spent on personal health care costs in the United States was devoted to care of individuals in their last year of life." ($221 billion) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4638261/