Jacques Barzun's 2000 From Dawn to Decadence: 500 Years of Western Cultural Life 1500 to the Present:
What is the reasoning behind exclusion and persecution? The keener the individual conscience, the sharper its judgment of human beliefs and behavior, its own included. In proportion to its "love of truth and hatred of sin," it develops suspicion of others' faith and morals. The smallest divergence from the absolute is grave error and wickedness. From there it is a short step to declaring war on misbelievers. When faith is both intellectual and visceral, the overwhelming justification is that heresy imperils other souls. If the erring sheep will not recant, he or she becomes a source of error in others.
Tags: Barzun, Dawn to Decadence, Faith