From Erasmus of Rotterdam by Stefan Zweig:

Only when the impulse to violence is inspired with an idea, or is made to serve an idea, do genuine “tumulti” occur. Then come the bloody and destructive revolutions, then the bands of ragamuffins get formed into a party hastening to obey the rallying-cry, then by organization is an army created, then does a dogma help to promote a movement. All the great and vehement conflicts that have arisen among men are more rightly described as the outcome of certain ideologies than as being due to the violence and bloodthirstiness of the human animal; for an idea may let loose the will to violence and drive it to the attack. Fanaticism, the bastard begotten out of brain and power, fancies itself dictator in the realm of thought, so that only what it thinks is acceptable and must be forced upon the whole universe; it thus splits the human community into friends or foes, adherents or opponents, heroes or criminals, believers or heretics; since it recognizes no other system than its own and no other truth than its own, it needs must resort to violence in order to curb and bridle the divine multiplicity of phenomena and to bring everything under one yoke. The forcible curtailment of mental latitude, of freedom of opinions, every kind of inquisition and censorship, of scaffold and stake – these evils were not brought into the world by blind violence, but by rigidly staring fanaticism, that genius of one-sidedness, that hereditary enemy of universality, that captive of a single idea which would shut the whole world up in a cage.