C.S. Lewis

"Theocracy is the worst of all governments. If we must have a tyrant, a robber baron is far better than an inquisitor. The baron's cruelty may sometimes sleep, his cupidity at some point be sated; and since he dimly knows he is doing wrong he may possibly repent. But the inquisitor who mistakes his own cruelty and lust of power and fear for the voice of Heaven will torment us infinitely because he torments us with the approval of his own conscience and his better impulses appear to him as temptations...

The nearer any government approaches to Theocracy the worse it will be. A metaphysic, held by the rulers with the force of a religion, is a bad sign. It forbids them, like the inquisitor, to admit any grain of truth or good in their opponents, it abrogates the ordinary rules of morality, and it gives a seemingly high, super-personal sanction to all the very ordinary human passions by which, like other men, the rulers will frequently be actuated. In a word, it forbids wholesome doubt. A political programme can never in reality be more than probably right."

Courtesy of Andrew Sullivan's outstanding site.