Argument: Unconstitutional to require individuals to buy private insurance
David B. Rivkin Jr. and Lee A. Casey. "Illegal health reform." Washington Post. August 22, 2009: "But can Congress require every American to buy health insurance? In short, no. The Constitution assigns only limited, enumerated powers to Congress and none, including the power to regulate interstate commerce or to impose taxes, would support a federal mandate requiring anyone who is otherwise without health insurance to buy it."
Randy Barnett, Nathaniel Stewart and Todd Gaziano. "Why the Personal Mandate to Buy Health Insurance Is Unprecedented and Unconstitutional." The Heritage Foundation. December 9, 2009: "A mandate requiring all individuals to purchase health insurance would be an unprecedented form of federal action. The government has never required people to buy any good or service as a condition of lawful residence in the United States. An individual mandate would have two features that, in combination, would make it unique. First, it would impose a duty on individuals as members of society. Second, it would require people to purchase a specific service that would be heavily regulated by the federal government.
[...] An individual mandate to enter into a contract with or buy a particular product from a private party, with tax penalties to enforce it, is unprecedented-- not just in scope but in kind--and unconstitutional as a matter of first principles and under any reasonable reading of judicial precedents."