All of us cherish our beliefs. They are, to a degree, self-defining. When someone comes along who challenges our belief system as insufficiently well-based - or who, like Socrates, merely asks embarrassing questions that we haven't thought of, or demonstrates that we've swept key underlying assumptions under the rug - it becomes much more than a search for knowledge. It feels like a personal assault.
Hitler and Mussolini were only the primary spokesmen for the attitude of domination and craving for power that are in the heart of almost everyone. Until the source is cleared, there will always be confusion and hate, wars and class antagonisms.
I do all the evil I can before I learn to shun it? Is it not enough to know the evil to shun it? If not, we should be sincere enough to admit that we love evil too well to give it up.