It is the bad people who need to have principles to restrain them. For one thing, he liked to hurt people. It was for the strange reason that he was cruel, that the poor fellow never killed a man who asked for mercy, or committed a cruel action which he could have prevented. One reason why he fell in love with Guenever was because the first thing he had done was to hurt her. He might never have noticed her as a person, if he had not seen the pain in her eyes.
People have odd reasons for ending up as saints.
A man who was not afflicted by ambitions of decency in his mind might simply have run away with his hero's wife, and then perhaps the tragedy of Arthur would never have happened. An ordinary fellow, who did not spend half his life torturing himself by trying to discover what was right so as to conquer his inclination toward what was wrong, might have cut the knot which brought their ruin. He was a kind, conscientious, peace-loving fellow, who had been afflicted in his youth by a tutor of genius. Between the two of them they had worked out their theory that killing poeple, and being a tyrant over them, was wrong. To stop that sort of thing, they had invented the idea of the Table a vague idea like democracy, or sportsmanship, or morals and now, in the effort to impose a world of peace, he found himself up to the elbows in blood.