The Difference Between Morality and Political Legitimacy

I take Rawls' theory to be an attempt to show how the central elements of a liberal democratic constitution are to be justified. And that requires him to say something about the grounds of the basic rights and liberties. So I think what's interesting there is this distinction between morality and political legitimacy. It seems like if Rawls' position is not going to address whether we should have those kinds of laws, then it's just incomplete.