Marxism is usually against religion, but it also isn’t utopian, it recognizes (indirectly) that it’s basically impossible to eradicate. Someone will always be suffering no matter how autonomous and luxurious and gay the communist society is. There will always be some sort of opium for the masses as a result.

I say usually because there have been self proclaimed Marxists who did great damage to the movement by being obsessed with religion like Pol Pot or random hippie terrorists who casually read Marx and think abusing their members is revolutionary

Though Marx is ultimately anti religion, there are several passages in which he laments the corruption of religion. That it’s supposed to be the worship of god, but instead it has been captured and repurposed into the worship of man and capital with a supernatural guise.