This is why I said that insurance companies should be able to charge more for things like smoking (they can), and without insurance in the US you have to pay for your treatment anyways. It is currently illegal in the US to not have insurance, so not being able to pay high costs shouldn't be a significant issue. As well, It is well within the governments right to charge for medicaid if they wanted to punish smokers for smoking, or people for living unhealthy lifestyles. A tax is not needed.
I understand your point, but it's not true that those without insurance in the US have to pay for their treatment. They owe money to the hospital that treated them, but they often don't pay it. Hospitals are not allowed to refuse service for emergency care. Additionally, while it is illegal in the US to not have insurance, the penalty is a small tax penalty, and the law doesn't stop a lot of people from still not owning insurance of some kind. I do think insurance companies should be able to charge more for things than smoking, but I think, while maybe not needed, a tax would help the problem even more.