Did Roberts bend under peer pressure?
...Progressives gain status and profit from expanded judicial power and from flexible constitutional rules, because they gain the ability to use the Supreme Court to trump voters’ and legislators’ decisions.

Much of the evidence for a Robert surrender consists of language in the so-called “dissent” written by the minority of four conservative judges.

The dissent includes language referring to the majority opinion as the “dissent.”

That “dissent” term is normally applied only to the minority’s explanation of their votes.

The likeliest explanation for the mismatched terminology is that Roberts initially joined the group of four conservative judges who wished to strike down the law. His vote made them the majority, and allowed them to label the progressives’ opinion as the minority dissent....

More Hints that Roberts Switched his Vote
...UPDATE: Ed Whelan notes a related theory: Roberts assigned the opinion to himself, and wrote most of what became the four-Justice dissent. He then switched on the tax issue, and the four dissenters adopted most of his original majority opinion as a dissent. This would explain why the dissent is unsigned. Other blogs are noting that Justice Ginsburg directs much of her ire at the Chief, which is the sort of things Justices do when they think they’ve lost someone’s vote, not when they are trying to keep a tenuous vote to uphold uphold the law in question on board....