>Sure everyone is entitled to their vice, but should we provide healthcare to people that are consciously, actively destroying their own health? Should we treat lung cancer in smokers? Should we treat diseases in anti-vaccers?

I think you are right that some people do take it too far. But from what I've seen a lot of people who do end up chain smoking or overeating processed foods daily have other underlying health-conditions. For example with smoking a lot of ADHD sufferers who are undiagnosed might self medicate with nicotine as it is a stimulant. Some might also have working memory issues and struggle with self control.

Ultimately most individual choices have a societal aspect to them, a lot can be tackled by education, early diagnosis and choice architecture