Nfgo3 is right. In addition, it’s important to keep in mind that Obamacare is basically the same as Romneycare, and the individual mandate was originally proposed by conservatives and libertarians in the 80s or 90s. Conservative Republicans proposed something similar back in the 90s when President Clinton almost passed universal health care. Ironically, everyone agrees that if the government simply passed Canada-style health care (Medicare for all), there would be no constitutional problem with it at all. even though it’s much closer to real “socialized” medicine. It has to do with which section of the constitution is at issue.
As an attorney who has read numerous state and federal supreme court decisions, I can tell you that a supreme court justice’s political preferences do not always predict which side they vote for in a case. For example, Justice Scalia often votes with the liberal justices on 6th Amendment issues, and Justice Breyer (a hard core liberal) often votes with the conservative justices in the same 6th Amendment cases.