Matt Yglesias and several of his commentators observe that nothing in constitutional law demands a limiting principle to the commerce clause or, in fact, to any enumerated power. Perhaps the framers didn’t intend Congress to impose its will on any domain of life through taxation and regulation of commerce, but if that was the founders’ intention, they simply fucked up in writing the Constitution. (Who said the Constitution can’t possibly contain mistakes?) The commerce clause allows regulation of international and interstate commerce; if it’s found that nothing in modern life stands outside of interstate commerce anymore, then nothing stands outside Congress’s enumerated powers. That the founders didn’t foresee this evolution in the 1780′s doesn’t obligate us to invent new limitations.
More broadly, Matt and other commentators note that plenty of bad, liberty-infringing laws are perfectly constitutional. There’s no special obligation to limit the commerce clause to preclude such laws, and very importantly, this is no big deal. The primary protections of liberty afforded by the Constitution are in its explicit prohibitions, such as in the Bill of Rights, and in the political process it guarantees. As the McCulloch v Maryland ruling noted, the general protection against tyranny afforded by the Constitution is the electoral process. You don’t want Congress to force you to eat broccoli? Don’t vote for that Congress.