Here’s a beautiful (albeit harrowing) passage from Meslier’s Superstition in All Ages:
What light could have been thrown into the minds of many famous thinkers, if, instead of occupying themselves with a useless theology, and its impertinent disputes, they had turned their attention upon intelligible and truly important objects. Half of the efforts that it cost the genius that was able to forge their religious opinions, half of the expense which their frivolous worship cost the nations, would have sufficed to enlighten them perfectly upon morality, politics, philosophy, medicine, agriculture, etc. Superstition nearly always absorbs the attention, the admiration, and the treasures of the people; they have a very expensive religion; but they have for their money, neither light, virtue, nor happiness.
Photo credit: Wikimedia Commons: http://en.wikipedia.org/wiki/File:Meslier.jpg