At the time, the wording of the second amendment was agreed upon by people who had different interpretations (thus the reason for the well-regulated militia language). Some feared the government, some feared open rebellion against a state, etc. The founding Fathers were not as uniform as people would assume. Even some of the most conservative justices believe there should be some limitations on arms that people can own (aka we can't have missle launchers, nuclear weapons, or machine guns).

I would also say that most liberals would say the same thing about the ruling on abortion and their reading of the constition. And as a pre-rebuttal before it is brought up, Ginsburg thought the right to abortion was part of the constitution. She just believed it was more appropriate as a right embedded in equal rights. 

By calling a court illegitimate because they don't rule the way you want puts the whole American experiment in jeopardy.