There is just as little doubt in the Christian fundamentalist world as there is in the Muslim fundamentalist world. So that was a fatuous statement, especially coming from a philosopher.Far more pertinent, and accurate, is Eric Hoffer's point, from "The True Believer," that fanatics and fundamentalists of whatever stripe have more in common with each other than they do with any other kind of believer.
I have to say, as someone who wrote regularly for The Inquirer's Faith Life section for years, the Christian fundamentalists never lived up to their fanatical billing. The only ones who came close -- and it was sometimes pretty close -- were those Young Earthers, who thought the Earth was made in six 24-hour periods some 5,000 years ago. Fundamentalism, after all, only refers to a movement to return to the "fundamentals" of Christianity. That said, Hoffer's point is well taken and is applicable all round.