I always considered myself agnostic leaning atheist. I consider leftism to be antithetical towards religion. All religions have a class structure to them, do priests, rabbis, or imams not exist? And what about marxism, is karl marx not venerated by some leftists in a weird atheist sort of way?
In this context he meant opium as medicine though. Right?
Not medicine, but as a pain reliever.
Sounds like it's pain relief considering, "heart of a heartless world, and the soul of soulless conditions."
No, it won't solve the problems, and is not medicinal. It can only reduce the pain. Look at the next two lines, and the last line most of all-criticism of religion is only the start.