From A Little History of Religion by Richard Holloway:
If daring to know how nature worked was one of the impulses of the Enlightenment, another was disgust with centuries of religious violence. Superstition was bad enough. War was worse. The thinkers of the Enlightenment noticed how religions always disagreed with each other. Each believed it possessed the truth revealed by God and the others were wrong. And when it got control of a country it tried to make everyone march to its drumbeat. That was bad enough. It was worse if there were just two religions in a country competing against each other. They would be at each other’s throats all the time, as they had been in Europe since the Reformation. But if there were thirty religions they all seemed to live in peace!