Do you know what he meant by "opiates of the masses?"
Here's the actual quote.
"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
A criticism of religion? Yeah, but what he was basically saying is that due to economic woes the masses being the down trodden, the poor and the unwealthy, turn to religion for solace. He's not necessarily saying down with religion, but saying that it shouldn't be a crutch for people to lean on during tough times. Marx, of course wanted everyone to be equal, if everyone wasn't suffering they wouldn't rely on just their religion to get out of it and maybe actually, do something.