Citizens can have their own grounding in their comprehensive doctrines, whatever they happen to be.

Of course, we know that not everyone agrees with assisted suicide, but people might agree that one has the right to it, even if they're not themselves going to exercise it.

The principles of justice are chosen behind a veil of ignorance.

There are two kinds of comprehensive doctrines, religious and secular. Those of religious faith will say I give a veiled argument for secularism, and the latter will say I give a veiled argument for religion. I deny both. Each side presumes the basic ideas of constitutional democracy, so my suggestion is that we can make our political arguments in terms of public reason. Then we stand on common ground. That's how we can understand each other and cooperate.

Ideally a just constitution would be a just procedure arranged to insure a just outcome.

Now the good of political life is a great political good. It is not a secular good specified by a comprehensive doctrine like those of Kant or Mill. You could characterize this political good as the good of free and equal citizens recognizing the duty of civility to one another: the duty to give citizens public reasons for one's political actions.

How did Madison get separation through Virginia and later Congress? The Baptists, the Presbyterians, and the smaller sects hated Jefferson; to them he was a secularist of the worst kind. But Madison could get Jefferson's bill passed because the Baptists, the Presbyterians, and smaller sects who were excluded in New England and in the South got together for their own protection.