To: Commie Basher
The Jews themselves have been guilty of fanaticism, for example when they killed every man, woman, and child in God's name, and even all the domestic animals, when entering Caanan.
The Spanish Inquisition wasn't an "odd" institution, it had the support of the Spanish people and government. They considered Judism a "cult," and happily murdered anyone who wouldn't "voluntarily" convert to Christianity.
The same thing happened with the Christian Crusades, hundreds of thousands of Christian fanatics killing heathen Moslems and Jews by God's holy name.
You would do better to ask "what is it about peace-loving religions that has spawned so many violent fanatics?"
The answer is that religions are not composed of saints, they're made up of ordinary people who sometimes get carried away by their beliefs, or get deceived by corrupt leaders.
Of course all human institutions, religious and secular, are prone to error, evil, and even violence. Duh!