Because, without knowing what is written up above, none of us knows what we want or what we are doing, and we follow our whims which we call reason, … - Denis Diderot

As to all the outward signs that awaken within us feelings of sympathy and compassion, the blind are only affected by crying; I suspect them in general of lacking humanity. What difference is there for a blind man, between a man who is urinating, and man who, without crying out, is bleeding? And we ourselves, do we not cease to commiserate, when the distance or the smallness of the objects in question produce the same effect on us as the lack of sight produces in the blind man? All our virtues depend on the faculty of the senses, and on the degree to which external things affect us. Thus I do not doubt that, except for the fear of punishment, many people would not feel any remorse for killing a man from a distance at which he appeared no larger than a swallow. No more, at any rate, than they would for slaughtering a cow up close. If we feel compassion for a horse that suffers, but if we squash an ant without any scruple, isn’t the same principle at work?

You spit on a petty thief, but you can't withhold a sort of respect from a great criminal. His courage bowls you over.
His brutality makes you shudder. What you value in everything is consistency of character.

From fanaticism to barbarism is only one step.