Adam Serwer has done excellent blogging on the court challenges to the Affordable Care Act, and I recommend you read it all, but I wanted to highlight this particular point:
My personal belief is that Republicans hate the law and want to see it gone, and so the conservative justices on the court, with the possible exception of Anthony Kennedy, will happily oblige them. The justices' identities are simply more partisan than we acknowledge -- does anyone remember Scalia decrying the 17th Amendment before it became a Tea Party cause?