The question of religion is haunting the left: the great finish to the French Revolution, and then to the generation of Hegel left everyone in a frenzy to embrace positivism and scientism, and in a way the marxist project was undone at the start by that contraction. It is obvious that Marx and Engels sensed the problem and their sideshow of the dialectic shows a wish to escape the Iron Cage descending on everyone.
We need to move on and the left should enlarge the scope of study to include religion, and far more than that. We live in a new world: the realm of the New Age movement has reintroduced witchcraft into culture. Being an historical materialist in that context is almost ridiculous. I am not advocating religious belief or new discussions about god, but a sense of the larger context of modernism which has more or less what is needed.