Fundamentalism is inherently a threat to freedom of thought

From Kindly Inquisitors: The New Attacks on Free Thought by Jonathan Rauch.

Fundamentalism, properly understood, is not about religion. It is about the inability to seriously entertain the possibility that one might be wrong. In individuals such fundamentalism is natural and, within reason, desirable. But when it becomes the foundation for an intellectual system, it is inherently a threat to freedom of thought.