From Roberts' opinion:
The text of a statute can sometimes have more than one possible meaning. To take a familiar example, a law that reads “no vehicles in the park” might, or might not, ban bicycles in the park. And it is well established that if a statute has two possible meanings, one of which violates the Constitution, courts should adopt the meaning that does not do so. Justice Story said that 180 years ago: “No court ought, unless the terms of an act rendered it unavoidable, to give a construction to it which should involve a violation, however unintentional, of the constitution.” Parsons v. Bedford, 3 Pet. 433, 448–449 (1830). Justice Holmes made the same point a century later: “[T]he rule is settled that as between two possible interpretations of a statute, by one of which it would be unconstitutional and by the other valid, our plain duty is to adopt that which will save the Act.” Blodgett v. Holden, 275 U. S. 142, 148 (1927) (concurring opinion).
Justice Roberts used this weak argument to prop up a law that most of the citizens of this country want to see repealed. He's lost all credibility to me. He simply changed the law to match the Government's THIRD argument - that the individual insurance mandate is a tax - no matter that Obama and all the other Democrats strongly argued it was not - and now it's the law of the land. That was not Congress' intent and it should not be taken as such because a mandated tax most likely would not have survived the vote.
From Justice Thomas' dissent (pointing out the Pandora's Box that Roberts just opened):
I adhere to my view that “the very notion of a ‘substantial effects’ test under the Commerce Clause is inconsistent with the original understanding of Congress’ powers and with this Court’s early Commerce Clause cases.” United States v. Morrison, 529 U. S. 598, 627 (2000) (THOMAS, J., concurring); see also Lopez, supra, at 584–602 (THOMAS, J., concurring); Gonzales v. Raich, 545 U. S. 1, 67–69 (2005) (THOMAS, J., dissenting). As I have explained, the Court’s continued use of that test “has encouraged the Federal Government to persist in its view that the Commerce Clause has virtually no limits.” Morrison,
supra, at 627. The Government’s unprecedented claim in this suit that it may regulate not only economic activity but also inactivity that substantially affects interstate commerce is a case in point.
http://www.supremecourt.gov/opinions/11 ... 93c3a2.pdf