One of my colleagues in law school has a textbook written by Randy Barnett, the main intellectual force behind the anti-Obamacare lawsuits. The textbook reportedly carries the following dedication:
To those who know that the Constitution of the United States is not what the Supreme Court says it is.
In this case, Barnett did get the court to agree with his reading of the Constitution. In reading the Court's opinion, it is clear that the "activity/non-activity" argument carried resonance:
Construing the Commerce Clause to permit Congress to regulate individuals precisely because they are doing nothing would open a new and potentially vast domain to congressional authority. Congress already possesses expansive power to regulate what people do. Upholding the Affordable Care Act under the Commerce Clause would give Congress the same license to regulate what people do not do. The Framers knew the difference between doing something and doing nothing. They gave Congress the power to regulate commerce, not to compel it. Ignoring that distinction would undermine the principle that the Federal Government is a government of limited and enumerated powers. The individual mandate thus cannot be sustained under Congress’s power to “regulate Commerce.”
Unfortunately for Barnett, that was not enough for Roberts to throw out the law, but now there is a new limit on the Commerce Clause.