"The case is easy and straightforward, however, in another respect. What is absolutely clear, affirmed by the text of the 1789 Constitution, by the Tenth Amendment ratified in 1791, and by innumerable cases of ours in the 220 years since, is that there are structural limits upon federal power—upon what it can prescribe with respect to private conduct, and upon what it can impose upon the sovereign States. Whatever may be the conceptual limits upon the Commerce Clause and upon the power to tax and spend, they cannot be such as will enable the Federal Government to regulate all private conduct and to compel the States to function as administrators of federal programs.
That clear principle carries the day here. The striking case of Wickard v. Filburn, 317 U. S. 111 (1942), which held that the economic activity of growing wheat, even for one’s own consumption, affected commerce sufficiently that it could be regulated, always has been regarded as the ne plus ultra of expansive Commerce Clause jurisprudence. To go beyond that, and to say the failure to grow wheat (which is not an economic activity, or any activity at all) nonetheless affects commerce and therefore can be federally regulated, is to make mere breathing in and out the basis for federal prescription and to extend federal power to virtually all human activity."
-- dissenting opinion of Scalia, Kennedy, Thomas and Alito, JJ., NATIONAL FEDERATION OF INDEPENDENT BUSINESS ET AL. v. SEBELIUS, SECRETARY OF HEALTH AND HUMAN SERVICES, ET AL.