This seems very obvious to me - although I cannot really think how to prove it; and indeed it is not the kind of thing that can be proved.
It simply seems that no secular materialist perspective provides the social coherence and individual solidity necessary to hold the line on anything.
Whenever I think of any secular materialist perspective it is obviously socially destructive.
But what of non-monotheist religions? Types of paganism? Religions without a deity? Non-scriptural monotheisms such as The God of The Philosophers, of the perennial philosophy, or generic spirituality?
They seem too weak, incoherent, subjective, fluid and yielding to beat secular Leftism; and even after secular Leftism self-destructs then they would - I think - give way before any Scriptural monotheism which remained.