That intimate laughter between fellow professionals, which of all earthly powers is strongest to make men do very bad things before they are yet, individually, very bad men

From That Hideous Strength by C. S. Lewis.

This was the first thing Mark had been asked to do which he himself, before he did it, clearly knew to be criminal. But the moment of his consent almost escaped his notice; certainly, there was no struggle, no sense of turning a corner. There may have been a time in the world’s history when such moments fully revealed their gravity, with witches prophesying on a blasted heath or visible Rubicons to be crossed. But, for him, it all slipped past in a chatter of laughter, of that intimate laughter between fellow professionals, which of all earthly powers is strongest to make men do very bad things before they are yet, individually, very bad men.