As part of Bush v Gore, the court stated in its majority opinion that the court's decision in the case could never be cited as precedent in another decision.
But think about the sort of precedent that is set by that! If the court can decide whenever it wants that a decision cannot be used as precedent, then why would a slippery slope argument ever work in front of the Court? In the Obamacare arguments, the conservative justices (including, sadly, Kennedy and Roberts) were focused on the things that could come after a decision in favor of Obamacare, such as mandated broccoli or burial insurance.
But those arguments are absolutely irrelevant in a post-Bush v Gore world! The court can just say its Obamacare decision can't be cited as precedent, and they could still choose to find mandates for broccoli or burial insurance unconstitutional.
This could apply to any other slippery slope argument. Gay marriage can't lead to incest or "man-on-dog" because any decision can declare itself unable to be cited.
Based on the oral arguments over Obamacare, the decision in the Obamacare case will come down to whether Roberts and/or Kennedy can come up with a limiting principle that would allow Obamacare but prevent broccoli. Why can't Bush v Gore give them that principle?