Incorrect use of OTC drugs; crossing the road while diddling a mobile phone; drinking alcohol; hell, pushing your toddler on a swing in a playground. Perhaps socialized medicine should refuse to treat people who have declined vaccination, or declined a bowel cancer screening. Maybe climbing a ladder should close you off from socialized medical care. Perhaps you shut yourself out if you ever hang out with sick people.
Obviously, I'm not serious.
For me, the big thing about socialized medicine is that it's universal. It's a massive benefit to everyone, if people with people with infectious diseases like TB, diphtheria and cholera can get treatment for free, without producing ID or proof of entitlement. And that's true whether or not they have legal status, as immigrants or whatever.