Without naming names (there are too many), Marxian thinkers become less than critical, they become religious, when they address religion. They revert to a pre-Marxian, quattrocento, grasp of both science and religion, which fails to grasp the intimate relationship between both in the emergence of capitalism during that same century.
In fact religion did not exist prior to capitalism. What existed was a bewildering variety of animisms. Spirits occupied every thing. And literally every thing was spiritual. The revolution we call the Reformation was a response to, not the author of, the birth of religion. For it was here, for the first time, that religious practitioners first deprived bodies of their spirits and spirits of their bodies. Finally, after so many centuries of darkness and bondage, the spirit was freed from its body. Religion in its full disembodied sense was born.
Science is not simply the flip-side of religion, the disenchanted body. Science is the logic of capitalism applied to bodies. It deprives bodies their spiritual voice. It compels bodies to speak logically, rationally, mathematically. It is then from the vantage point of this disenchanted body that Marxian thinkers often critique their co-religionists, the religious, whose spirit they fail to recognize as their own.
In a non- or post-capitalist world, bodies would recover their spirits and spirits their bodies. And polytheism would once again reign. But religion in its modern sense would entirely disappear. Or perhaps it would be remembered as that insane moment in history, from roughly 1324 to 2050, when we were compelled to hear the world in the foreign language of pure mathematics.