Preventing people from doing unhealthy things to themselves is in the public interest. I don't personally care if people smoke (though it significantly lowers my opinion of them), as long as it happens well away from me. But more sick people increases medical costs for everybody else.
The fact that our medical system is structured in such a way that individual health costs are externalized onto everyone else is a problem in itself. It would be better to seek to change that rather than restrict personal freedom and choice.
No. No, no no no. Sorry, Yellow Avatar, but societal sharing of medical expenses is extremely necessary. Otherwise people who have chronic health problems get raped by medical bills, meanwhile those who won the DNA lottery are set for life. This is exactly why the clause that banned 'pre-existing conditions' precluding you from coverage is one of the most popular parts of Obamacare.