"To do evil a human being must first of all believe that what he’s doing is good . . . Ideologythat 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 others’ 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. Alexandr Solzhenitsyn, The Gulag Archipelago.
“Military necessity does not admit of crueltythat is, the infliction of suffering for the sake of suffering or for revenge, nor of maiming or wounding except in fight, nor of torture to extort confessions.” - Abraham Lincoln's General Orders, 100 Instructions for the government of the armies of the United States in the field.