The crux of the distinction for me is that on the one hand, functional religions are informed by all the centuries of organic wisdom and tradition built up by a people, whereas socialism is a set of abstract, pie-in-the-sky utopian ideals that conceptualizes all humans as identical in their fundamental nature and malleable in their behavior.

To be fair: the people who came up with those ideals understandably did not foresee them being applied to rationalize things like urinating on each other at pride parades to own the Christians.