Aleksandr Solzhenitsyn quote from "The Gulag Archipelago"

To do evil a human being must first of all believe that what he’s doing is good, or else that it’s a well-considered act in conformity with natural law. Fortunately, it is in the nature of the human being to seek justification for his actions.

Macbeth’s self-justifications were feeble – and his conscience devoured him. Yes, even Iago was a little lamb too. The imagination and the spiritual strength of Shakespeare’s evildoers stopped short at a dozen corpses. Because they had no ideology.

Ideology – that is what gives evildoing its long-sought justification and gives the evildoer the necessary steadfastness and determination. That is the social theory which helps to make his acts seem good instead of bad in his own and other’s eyes, so that he won’t hear reproaches and curses but will receive praise and honors. That was how the agents of the Inquisition fortified their wills: by invoking Christianity; the conquerors of foreign lands, by extolling the grandeur of their Motherland; the colonizers, by civilization; the Nazis by race; and the Jacobins (early and late), by equality, brotherhood, and the happiness of future generations.

Thanks to ideology, the twentieth century was fated to experience evildoing on a scale calculated in the millions. This cannot be denied, nor passed over, nor suppressed. How, then, do we dare insist that evildoers do not exist? And who was it that destroyed these millions? Without evildoers there would have been no Archipelago.

– Aleksandr Solzhenitsyn