From a must-read piece on the Roberts Court by Garrett Epps:
Against these more recent arguments, the chief justice upheld the mandate as a tax because, as far as he could tell, it is a tax—and a tax is, in fact, what it is. Koppelman shares Tushnet’s conviction that Roberts “was conscientiously trying to do the best job he could.” That explanation does not satisfy Josh Blackman, a professor at South Texas College of Law. Blackman has written a deeply researched, highly readable account of the conservative challenge to the ACA, which, as a recent law graduate, he witnessed from the inside; Unprecedented: The Constitutional Challenge to Obamacare includes an introduction from its own hero, Georgetown law professor Randy Barnett. The intellectual godfather of the challenge, Barnett has been pleading the libertarian case to the Court for years (he argued and lost Gonzales v. Raich, in which he contended that Congress could not regulate personal possession of medical marijuana). His scholarship lays out a truly radical view of government and the Constitution. In The Tough Luck Constitution, Koppelman writes that Barnett “wants to privatize schools, prisons, courts, streets, parks, and the police.”
Barnett attained legal rock-star status by creating the “activity/inactivity” argument more or less out of thin air. (Koppelman calls him, in genuine admiration, “the most successful legal rhetorician since Catharine MacKinnon,” the creator of sexual-harassment law.) After the mandate was upheld, Barnett angrily dismissed Roberts’s opinion as “political, rather than legal.” Blackman writes acerbically, “Roberts rewrote the most controversial provision of the ACA,” affirming “a statute that Congress did not write.”
No one could suspect either Barnett or Blackman of crass partisanship—that is, of wanting the mandate struck down to boost the electoral chances of Mitt Romney, say, or to help Republicans retake Senate control. Both men are serious, committed scholars, and their anger arises out of principle: Roberts abdicated what they see as the proper role of a libertarian Court.