National defense, i.e. the military, is a single payer system. We seem to have no problem with that. The government pays and private firms make the tanks, bombs, planes and ships.
Why can't we make national health care, for everybody, a single payer system? We can, it's just a matter of priorities.
A healthy citizenry is an invaluable asset, just like national defense is. We could have both; there is no shortage of dollars.
Does the government require citizens to buy "defense insurance?" No, it just pays for everyone's defense.