I know that's the argument, but I disagree with the premise -- you're essentially saying that it's valid for the government to enforce healthy decisions when it wants to limit the chances of a future payout. This would mean that the government can use its status as the "insurer" (in the sense that it operates the safety net) and the "enforcer" (in the sense that it alone can use force to compel you against your will) in complementary ways. Why not make a law that I can't have junk food? Or that I must exercise? Obesity has a cost on society as well, no?