The separation of church and state is necessary partly because if religion is good then the state shouldn’t interfere with the religious vision or with the religious prophet. There must be a realm of truth beyond political competence, that’s why there must be a separation of churches. But if religion is bad, and a bad religion is one that gives an ultimate sanctity to some particular cause, then religion mustn’t interfere with the state. So one of the basic democratic principles as we know it in America is the separation of church and state.

Reinhold Niebuhr (1892-1971) American theologian and clergyman

Interview with Mike Wallace (27 Apr 1958)

Full text.