“I am a democrat because I believe that no man or group of men is good enough to be trusted with uncontrolled power over others. And the higher the pretensions of such power, the more dangerous I think it both to the rulers and to the subjects. Hence 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. And since Theocracy is the worst, 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 other words, it forbids wholesome doubt. […]
This false certainty comes out in Professor Haldane's article. […] It is breaking Aristotle's canon—to demand in every enquiry that the degree of certainty which the subject matter allows. And not on your life to pretend that you see further than you do.
Being a democrat, I am opposed to all very drastic and sudden changes of society (in whatever direction) because they never in fact take place except by a particular technique. That technique involves the seizure of power by a small, highly disciplined group of people; the terror and the secret police follow, it would seem, automatically. I do not think any group good enough to have such power. They are men of like passions with ourselves. The secrecy and discipline of their organisation will have already inflamed in them that passion for the inner ring which I think at least as corrupting as avarice; and their high ideological pretensions will have lent all their passions the dangerous prestige of the Cause. Hence, in whatever direction the change is made, it is for me damned by its modus operandi.”

The worst of all public dangers is the committee of public safety.
"A Reply to Professor Haldane" (1946), published posthumously in Of Other Worlds: Essays and Stories (1966)
Some of these ideas were included in the essay "The Humanitarian Theory of Punishment" (1949) (see below).