Quote shamelessly lifted from that excellent blog, The Ironic Catholic.
When such a critic says, for instance, that faith kept the world in darkness until doubt led to enlightenment, he is himself taking things on faith, things that he has never been sufficiently enlightened to doubt. That exceedingly crude simplification of human history is what he has been taught, and he believes it because he has been taught. I do not blame him for that; I merely remark that he is an unconscious example of everything that he reviles.
--G.K. Chesterton [Source]