What I call Platonism is often impilict and may even be denied by its believers - but I think it is a religion, and it does affects people's lives and behaviours, albeit in an individualistic manner (since there is no church of Platonism).
By Platonism, I mean the belief that behind the everyday, up-front and obvious world of differences and changes and incomprehensible complexity; there is a world of simpler, eternal and unchanging 'forms' - and this world of forms is more real than the everyday world because we can have genuine knowledge of it (whereas the everyday world of change lacks pattern, and is unknowable).
By such a definition, Platonism has been the implicit religion of many of the greatest mathematicians and scientists, of many artists and scholars - and in general many of those who inhabit the world of the mind.
Platonism may be Christian, or non-Christian - in fact, Platonism has been the basic world view of the majority of Christian intellectuals since at least the middle second century AD (although there is very little evidence it in the Old or New Testament - and none of that evidence is clear or explicit).
But Platonism has been, in fact, the secret religion of the majority of intellectuals full stop.
Whether this has anything to do with the specific lineage of Plato, or whether Platonism is a basic archetypal pattern of thinking into-which intellectuals tend to fall (a 'strong attractor' as it were) - I am not sure.
And although Platonism has been probably dominant religion of serious intellectuals, it is not necessary nor inevitable as the religion of real intellectuals - there are other equally coherent and motivating alternatives; such as Aristotelianism (a significant modification of Platonism - focused on the primacy of universal forms, rather than a separate world of forms).
But Platonism is dominant among serious intellectuals, probably because if a serious intellectual is not a Platonist, the philosophy will probably not be strong enough to work as a real religion. So an Aristotelian must be primarily a Christian (or some other type of monotheist) if he is to stay honest and true.
And the same would apply to a pragmatist pluralist such as myself - we could only stay honest if our pragmatism is underpinned by strong, binding, personal monotheism. I think it is too easy for non-Platonists to become corrupted by worldly-things unless they (we) are underpinned by monotheism.
In this sense, Platonism is the strongest of all philosophies
Platonism is the only philosophy which can serve as a way of life, as the bottom-line for living.
Even nowadays, and even among those rare and few real scientists who self-describe as non-religious, Platonism is a strong, bottom line, metaphysical religion - as is most obvious when top-notch mathematicians (such as Roger Penrose^) discuss their basic stance and the meaning of their work.
This basic conviction about the nature of reality is - for such people - an important motivation and source of strength and honesty; because it enables then to resist the usually- irresistible worldly considerations of money, career, awards, peer status etc: the Platonist intellectuals regard themselves as working for eternity - their 'reward' for unworldly disinterestedness will be in Platonic Heaven, and will endure long after the expediencies and corruptions of everyday life have been swept away in this world of constant change.
And what is Platonic Heaven? The emphasis is impersonal; the Platonic God is not, primarily, a personal God with whom one has a personal relationship; he is an abstract God of abstract properties such as reality itself and the self-contemplation of reality; so Platonic Heaven is not a relationship but a state of being - some kind of bliss-full absorption in pure knowledge.
The Heavenly reward of the faithful Platonist is eternally to participate-in pure conscious awareness of exactly that eternal and unchanging reality which he has revered, and which he has served.
This is the hope which makes him brave, steadfast and honest in his dealings.
Yes, Platonism is a real religion, although rarer now in The West than at any time in the past 2000 years: Platonism is a real religion because Platonism makes a real difference.
^Here is a modern Platonist - perhaps the greatest living mathematical physicist - being explicit about his beliefs, convictions and motivations: