The problem is once you start saying things like universal healthcare shouldn't cover lung cancer for a chronic smoker, where do you draw the line? Suddenly people have to go through some kind of bureaucratic process to get treatment for things. Do you just have to wait without treatment while its processed? Will people be stuck in the same situation they have now of trying to decide if it's worth getting treatment for something and potentially going broke? Is the chronic smoker only denied treatment for lung cancer, or for other things too? What if during your cancer treatment application it comes out that you smoked cigarettes a few times when you were a teenager, do you no longer qualify? That wouldn't seem fair, but what if you smoked two packs a day for decades but then decided to turn your life around and quit? Where does that line get drawn? If a 600 pound patient is denied treatment for their heart disease, what BMI disqualifies people? Do you get treatment for diabetes if you're 5 pounds in the obese range? The cutoff has to be somewhere. What about accidents? Should I as a taxpayer have to help pay for someone's broken leg because they were doing a dangerous stake board move? It was their choice to stake board after all.

Trying to overfit your model to only allow those deemed innocent or deserving will not generalize well. There is bound to be unfairness. If it's decided that only the extreme cases will be denied, the two pack a day current smoker and the 600+ pound person, those cases are very rare. They aren't going to be a huge drain on the system. If their treatment was denied, yeah maybe you'd save $100K, but in the grand scheme of hundreds of billion dollars a year, it really doesn't matter. In my opinion, that potential savings of a fraction of a percent of the budget doesn't override my belief that everyone is entitled to care.