They passed a law legalizing same sex marriage and didn't seem to have much of problem forcing on all the states.
There’s a difference. As I said, the Court can only change the law 1 way - they can repeal existing laws, which is exactly what Obergefell, Roe v. Wade, Lawrence v. Texas, and countless other decisions have done. If something is legal that means there are no provisions against it. Obergefell got rid of existing provisions. There’s nothing in the constitution that can be reinterpreted so as to create a provision against certain kinds of weapons. It’s easier for government to do nothing than to enforce laws. Defying Obergefell requires enforcing laws, where defying a gun prohibition would require no action.
By the way SCOTUS recently upheld a Texas law denying marriage benefits to queer couples.
They passed a law legalizing same sex marriage
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No law was passed, the Supreme Court just decreed that we all had to accept it.