While the origins of religious belief are "primitive" in the sense of being pre-modern (Mark Sandell, "Resurgent religion threatens gains of struggle", Solidarity 308) the same can be said of many other things - music, mathematics, science.
What I think we need to do is distinguish both between religion and science and between different kinds of religion.
Religion in the pre-modern, "primitive" era tended to be almost exclusively polytheistic. The major monotheistic religions of Judaism, Christianity and Islam are all comparatively modern (a few thousand years old at most) and their political/fundamentalist forms very modern indeed.
The idea that "bereft of any explanatory power in the wake of scientific knowledge of the universe" religion is irrelevant wrongly implies that all religions see themselves as providing alternate theories about the origin of the universe to those provided by science as opposed to providing answers to questions in other fields such as morality and philosophy. I'm also not sure about the idea that "In modernity many of these roles are taken by secular science."
Much of the criticism of religion made by Dawkins et al has the tone of well-educated, middle-class people sneering at the poor because, as a priest put it to the person who recruited me to Socialist Organiser in the early 90's, "now you've been to college, you think you're too clever to believe in God."
Even if you don't believe in God and want to remove religious belief from society, do you think it is tactically wise for socialists to describe religion as "primitive" or "mumbo jumbo"?