According to Plaintiffs, the conduct regulated by the provision—the failure to purchase health insurance—is a decision not to engage in interstate commerce, and consequently it is not a form of activity; rather, it is better characterized as inactivity, or "simply existing." . . .The "similarly" refers to the facts addressed in Gonzales v. Raich, where regulations defended under the interstate commerce power were held to reach marijuana cultivated for private use, which at least is an activity, and therefore in an important sense dissimilar from deciding to not grow marijuana. The latter decision likewise would contribute to there being less marijuana and thus also having an effect on the national market for marijuana (although probably not as "substantial" an effect as Congress had shown with its figures relating to the cost of providing health care to the uninsured*).
I hold that there is a rational basis for Congress to conclude that individuals' decisions about how and when to pay for health care are activities that in the aggregate substantially affect the interstate health care market. . . .
Here, similarly, the choice of individuals to go uninsured affects national market conditions for health insurance, reducing the supply of consumers of health insurance who are in good health, and thereby increasing the cost of covering the insured population.
But, for the purpose of interpreting the language in the Constitution, it shouldn't make any difference whether the effect is measured in hundreds or hundreds of millions or even billions of dollars.
Liberty University v. Geithner (.pdf; 54 pgs.)
The Commerce Clause section is on pages 22 through 29. The district court does not expressly declare that the individual insurance mandate is a valid exercise of Congress's interstate commerce power, but only that Congress could reasonably conclude that it is.
'Not enough judicial activism,' some will complain.
* Or, more specifically, the higher cost of providing health care to the insured arguably caused by the substantial population of uninsured.