One of the most common beliefs about the way that John Roberts has voted on ObamaCare is that he's doing so to preserve the Supreme Court from ferocious attacks by the Liberal elite. Commentators beleive that Roberts caved to political pressure, fearing that opposing Obama and the left would "de-legitimize the Court."
There is no question that the major organs of public opinion would have been hysterical if ObamaCare had been gutted or gay marriage had not put on the same pedestal as abortion on demand.
So Roberts chose to protect the Supreme Court from the wrath of the New York Times and NPR. The Constitution was left to fend for itself.