Chief Justice Roberts comments on the limits of the Commerce Clause in the National Federation of Independent Business v. Sebelius (Obamacare) decision:
People, for reasons of their own, often fail to do things that would be good for them or good for society. Those failures—joined with the similar failures of others—can readily have a substantial effect on interstate commerce. Under the Government’s logic, that authorizes Congress to use its commerce power to compel citizens to act as the Government would have them act.
That is not the country the Framers of our Constitution envisioned. James Madison explained that the Commerce Clause was “an addition which few oppose and from which no apprehensions are entertained.” The Federalist No. 45, at 293. While Congress’s authority under the Commerce Clause has of course expanded with the growth of the national economy, our cases have “always recognized that the power to regulate commerce, though broad indeed, has limits.” Maryland v. Wirtz, 392 U. S. 183, 196 (1968). The Government’s theory would erode those limits, permitting Congress to reach beyond the natural extent of its authority, “everywhere extending the sphere of its activity and drawing all power into its impetuous vortex.” The Federalist No. 48, at 309 (J. Madison). Congress already enjoys vast power to regulate much of what we do. Accepting the Government’s theory would give Congress the same license to regulate what we do not do, fundamentally changing the relation between the citizen and the Federal Government.