More comments from Chief Justice Roberts on the limits of the Commerce Clause in the National Federation of Independent Business v. Sebelius (Obamacare) decision:

Everyone will likely participate in the markets for food, clothing, transportation, shelter, or energy; that does not authorize Congress to direct them to purchase particular products in those or other markets today. The Commerce Clause is not a general license to regulate an individual from cradle to grave, simply because he will predictably engage in particular transactions. Any police power to regulate individuals as such, as opposed to their activities, remains vested in the States.