Justices are NOT supposed to carry a desired outcome into a case. That's judicial activism. They are supposed to simply weigh each case on the merit of the law re: the Constitution. If the law clearly states, for instance, that federal subsidies are only to be given to exchanges founded by the states in accordance to a paragraph that defines those exchanges, they are not to reason, "I don't want to overturn this law, so I'll just pretend Congress didn't actually mean what they wrote".
For Obamacare: "Established by the state" clause over which the King v Burwell case was fought is clear. State means federal government or the state government.
Remember second amendment? "Security of free state" does not mean local state. State means the federal government. WHy don't the RWers object to that 2nd amendment and continue to demand that states should decide whether the guns are lawful.
The judicial activism means changing the laws. SCOTUS did not change any laws. W Obamacare, the SCOTUS kept the law as is and wants congress to pass the laws.
W regards to GM, this was a constitutional issue. Neither the states nor the fed government has the right to ban marriages between two adults who are not blood related. So marriage case was settled on the basis that individuals are free to marry one other non-blood-related adult of their choosing.
This is not judicial activism. This is simply respecting the individual's right. Actually activism means SCOTUS interfering with the legal proceedings, not "leaving it alone as is". Tampering is activism, leaving it alone is simply not activism. Unless of course tampering actually prrotects constitutional right....then it's not activism, it is called following the constitution.