You should pay because cancer caused by smoking is exceptionally expensive to treat effectively, whats more, if you don't want to pay more... stop smoking, and you'll have the benefit of living longer. Also people rarely intentionally do things that make them ill (in your example of somebody with an eating disorder... ok there exceptions as with everything in life). Smoking has a huge array of negative side effects more even than alcohol. Who said you'll get a different level of healthcare, everybody should receive the same, you'll just be paying more for it because you smoke.
If you think smoking is a human right... sorry, I don't agree. I do however agree with you that it is all about choices and consequenses... the concequence of smoking is that you're much more likely to get cancer so you should pay more. But at the end of the day it is all about money, if it were free to treat cancer patients, then there wouldn't be an issue.
And before anybody assumes I am discriminating against people who suffer with cancer, I'm not... I'm discriminating agains people who have cancer due to smoking. You may argue that thet may have got cancer anyway, which is true, but they wouldn't have had to pay extra to treat it.
EDIT: Just read fish dudes comments, lol, but actually why not, I'd rather that healthcare was properly privatised... but not the way it is in america (i.e. health care should be 'not for profit'), and certainly not the way it is now.