Logically of course it isn't the constitutionally guaranteed "republican form of government" when a state's constitution has no meaning, but court rulings are exempted from that clause- by the courts.
I guess one of their major argumement was that the MA constitution (uniquely) reserves questions of marriage to the Legislature. The First Circuit wouldn't intervene now, but will hear arguments in June. The Supreme Court wouldn't take it now (though it will undoubtedly hear it eventually).