Neither Hillary nor Barrack are talking about changing health care in this country to something resembling the UK's National Health Service nor the French system, which is a hybrid of public and private financing that works well for them.
Both Democratic candidates are talking about making insurance more accessible and affordable for americans. Outlawing the hated preexisting conditions and providing funds to help lower income folks afford premiums.
Hillary's health care proposal -
http://www.hillaryclinton.com/issues/healthcare/Barack's health care proposal -
http://www.barackobama.com/issues/healthcare/I genuinely wish we were talking about a US version of the British HS. That would be the humane thing. But we are far from that at this point.
As to your questions:
The obesity epidemic, almost entirely due to poor personal habits,...Obesity is caused by a variety of factors, not just poor personal habits. It's simplistic to think that everybody who is overweight just simply eats too much or eats poorly.
It has to do with our modern lifestyle, more driving in cars, less chance for exercise. Europeans in general walk much more than we do just because they are within walking distance of parks, entertainment, dining establishments. And they can take excellent public transportation to work. It's not necessary to drive everywhere. We, more often than not, have to drive to just about everywhere. We will have to rethink how we plan cities and downtowns and living areas so that we can get out of our cars more often. Human beings didn't evolve to be as sedentary as we are now in the US. We were designed for movement and physical work. Our bodies and metabolism reflect that.
As for poor eating, that is especially true if you live in a poor urban neighborhood. You likely don't have a good grocery store that sells good produce and other healthy items you can afford. It's cheaper to buy fast and snack food crap because that's what the local stores sell. Again, this is a matter of city and neighborhood planning. People without much money deserve good food at a reasonable price also. Not everyone who lives in a depressed area is a pimp or a drug dealer out on the make.
As for paying for self destructive behaviors, all groups of human beings have them. You will never get away from them. For example the UK has a well-known and well-documented drinking problem. But no one there, that I am aware of, is suggesting they outlaw alcohol and the venerable British pub.
People with drug addictions need care also. Substance abuse should be treated like the health problem it is, rather than a police/criminal problem.
As for a government trying to stop self-destructive behaviors, you can try to provide incentives for people to stay or get healthy, but that's about it.
We all need to be taking care of each other in this society. Not everyone is fully 100% capable 100% of the time. In short, there are aspects of human beings that make us quite frail in some ways. The thing I dislike most about the Libertarian viewpoint is that the owner of said POV usually assumes s/he will never need any help from anyone for anything. It's both selfish and short-sighted. No one likes to be ill, but it does happen. None of us knows our own futures. To think that you can control you life to omit illness or the need for doctors and medicine is to buy into a medieval mindset that illness is the price we pay for some unknown sin, that illness is a just punishment.
If the "treat them as you would treat yourself" argument doesn't work for you, think about my last point. I would gladly give the $800 Bil we annually give to the DoD to an American NHS. And you know what? It won't cost that much. Virtually every country that has national health care spends much less per person than we do and they get a far better ROI than we do.