"... paying 'cash for clunkers' is one thing; making everyone buy a Chevy is quite another"

...the Supreme Court has long allowed Congress to regulate and prohibit all sorts of "economic" activities that are not, strictly speaking, commerce. The key is that those activities substantially affect interstate commerce, and that's how the court would probably view the regulation of health insurance.

But the individual mandate extends the commerce clause's power beyond economic activity, to economic inactivity. That is unprecedented. While Congress has used its taxing power to fund Social Security and Medicare, never before has it used its commerce power to mandate that an individual person engage in an economic transaction with a private company. Regulating the auto industry or paying "cash for clunkers" is one thing; making everyone buy a Chevy is quite another. Even during World War II, the federal government did not mandate that individual citizens purchase war bonds.