The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
Where in the United States Constitution does it give the authority to the federal government (for example) to:
Legislate and regulate marriage
Legislate and regulate healthcare, to create commerce in order to regulate it
Legislate and regulate the right of the people to keep and bear arms
The Supreme Court has the authority to interpret laws that fall within the confines of the United States Constitution. All other matters are left to the States respectively, or to the people. Obamacare, DOMA, a federal registry for guns are all outside the confines of the US Constitution, no matter what the Supreme Court decides.