In “How the Freedom to Contract Protects Insurability” Paul Hseih makes the economic case and moral case for a free-market in health insurance. Here is just one choice quote:
It is true that patients today with preexisting medical problems can have difficulty purchasing health insurance. But forcing insurers to cover such patients is not the solution. On the economic level, such coercion would create many new problems. For instance, under such legislation patients would have a strong incentive to delay purchasing insurance until they got sick, knowing they could not be denied coverage at that time. Why pay for insurance before you need it if you can wait and purchase it when you need it? Thus, many people would simply go without insurance until they needed medical care, at which time they would purchase an insurance policy and receive immediate coverage far in excess of the price paid for the policy. Such laws would legalize plunder.
Required reading.