"Opiates are a type of analgesic meaning that they reduce or modulate the sensation of pain so that it (the pain) is more bearable..." Marx, I believe, chose this metaphor to describe how religion, with it's promise of hope in the after-life serves to make the pain of life more bearable and the masses more calm and controlled. The danger is that an opiate, like religion, can dull the senses. It calms society into accepting what they perceive is their fate since everyone dies and their reward is in heaven. Illustrations as to how this security blanket of religion and the hope of life after death plays out politically both in radical Eastern religions and radical Western religions are in the news daily. At the extreme, religion and it's after-life promise caused individuals to divert the basic instinct for their very own survival, reject a natural instinct for empathy, and fly planes into the World Trade Center and Pentagon. At it's slightly more moderate expression, at least in the short term, religion results in belief in Apocalypse which leads to apathy concerning human-kinds' present impact on issues of nuclear proliferation, global climate change, and disparity of distribution of wealth. At the most individual level, religion is what keeps us in the same pattern as our parents - the same socio-economic class and at the same level of accomplishment. It's the sighed resignation of "Well, that's it, ya know" and the embracing of contentment with "the way things are... because everything happens for a reason, doncha know?"