> 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.

That is, "opium" here is references a painkiller; religion is viewed as a way to deaden pain and suffering. It's not about addiction.