"Insurance" defines a behavior whereby a group of individuals agree to contribute to a pool of resources in order to provide protection to participating individuals in case of a costly event.
"Benefiting without contribution" is the definition of a parasite. Therefore, those who choose not to participate in health insurance should be willing to not receive emergency care unless they can prove they have the resources to pay for it, nor be provided any other health care for which they cannot pay.
Civilized behavior shows evidence of moral, ethical, humane and intellectual advancement, and many think this includes providing access to modern health care to those unable to afford it. If one considers the cost of repairing a compound leg fracture, they'll find most cannot afford even a basic modern procedure.
If not the current system, or the ACA, then what? Civilized people desire to provide health coverage for those who, at least temporarily, are not as fortunate. Perhaps parasitic behavior should be allowed, as long as those choosing this route understand they must pay or do without.