Who decides what disqualifies someone? Who defines the requirements? That is the problem, and what makes it not so simple. I could eat a perfectly healthy diet, never do drugs, never smoke cigarettes, but also never exercise and be less healthy than I could be. Should that disqualify me from coverage? Should eating fast food once a week disqualify me? Is it morally acceptable for the government or some other entity to keep track my lifestyle for the sake of making that decision?

It's a problem that sounds easy to solve on paper, but in practice it just isn't so simple.