An atheist can be a citizen, but he cannot be a good citizen. A good citizen does more than abide by the laws. A good citizen is able to give an account, a morally compelling account, of the regime of which he is part – and to do so in continuity with the constituting moment and subsequent history of that regime. He is able to justify its defense against its enemies, and to convincingly recommend its virtues to citizens of the next generation so that they, in turn can transmit the order of government to citizens yet unborn. This regime of liberal democracy, of republican self-governance, is not self-evidently good and just. An account must be given. Reasons must be given. They must be reasons that draw authority from that which is higher than ourselves, from that which transcends us, from that to which we are precedently, ultimately, obliged.
The American experiment in constitutional democracy was not conceived and dedicated by those who today call themselves “atheists,” and it cannot be conceived and dedicated anew by such citizens. In times of testing – and every time is a time of testing for this experiment in ordered liberty – a morally convincing account must be given. One may ask, Convincing to whom? One obvious answer in a democracy, although not the only answer, is that it must be convincing to a majority of citizens. Minorities, including the minority of atheists, are assiduously to be protected in their legal right to dissent. It is the responsibility of their fellow citizens to give a moral account – an account that atheists cannot give – of why that is the case. Giving such an account in continuity with the truths by which this political order was constituted is required of good citizens, not least because those who cannot give such an account depend on others who can.
American Babylon: Notes of a Christian Exile (pp. 116, 118)