People who abuse their bodies ought to pay for their abuses.
My concern purely falls on those who get caught in the crossfire. This is why I'm in support of a public smoking ban (because a smoker is causing harm to others). Drugs and alcohol are a different issue as the 'damage' caused is due to actions caused by drug, rather than the drug itself in which case there are means to protect others (the police).
Going back to the topic, I cannot support government funding for those who've messed their own bodies up. In the context of obesity, however, there will be many people with various disorders that have no arising through any fault of their own. Perhaps they were born with it, or serious illness has rendered them incapable on normal weight control without medical intervention. It happens.
From here, we can go back to the perils of being in the disadvantaged / low SES section of the population.