Drinking Coke is now a sin? sin tax
If you can put a sin tax on alcohol then you can put one on soda.
Look, as long as we as a society have decided to treat diabetics rather than letting them die, then we should do something to encourage people to be healthy. Everyone (outside of congress) can agree that we should stop subsidizing corn so much because it drastically reduces the price of things like high fructose corn syrup, which reduces the price of cheap, sweet processed food and encourages poor people to buy terribly unhealthy food (because the price per calorie is so much less than veggies and fruit).
What to do beyond that is up for debate, but pragmatically speaking doing nothing is a bad option.