In beauty of face no maiden ever equaled her. It was the radiance of an opium-dream—an airy and spirit-lifting vision more wildly divine than the fantasies which hovered about the slumbering souls of the daughters of Delos.
Religious distress is at the same time the expression of real distress and the protest against real distress. Religion is the sigh of the oppressed creature, the heart of a heartless world, just as it is the spirit of a spiritless situation. It is the opium of the people. The abolition of religion as the illusory happiness of the people is required for their real happiness. The demand to give up the illusion about its condition is the demand to give up a condition which needs illusions.
Karl Marx, Critique of Hegel’s Philosophy of Right, 1843-4