Karl du Fresne: Heaven protect us from self-righteous zealots

We tend to think of idealism as a good thing. Idealists want the best for the world and for humanity – or so we assume. Who could possibly object to idealism, then? Yet idealism can be perverted. It can morph into zealotry and fanaticism. People can become so convinced of the correctness of their ideals that they feel able to justify almost any action aimed at fulfilling them.