Going with your explanation creates a weird situation where humanity is perfectly fine at first with believing in the existence of all kinds of magical beings, and then suddenly they are not.
But that is how it happens on the CV world, isn't it? Soma doesn't believe supernatural stuff until he has a hands on experience with it, DESPITE the world teeming with this around him. He believes it only when he has NO CHOICE but to believe it.
Also, I personally didn't get that from his explanation. Lumi's only explaining how people cope with holding specific beliefs in a world where everything is real. He's specifically talking about the CV world.
This is just my opinion but regarding the deniability argument, doesn't that run counter to history? Like I mentioned above, most of what is regarded today as supernatural was considered to be very much real in the past, up to the point that the existence of certan magical creatures was part of scientific consensus. But then, somehow, people started disbelieving for no particular reason?
Of course it doesn't run counter to history. I don't know where in the world you live, but where I live, the supernatural is common sense; Most people believe in stuff such as "miracles" and "prophets". Churches amass thousands of followers. The deeper you go inside a given state, the more ludicrous stories about supernatural sightings become. It's
EXTREMELLY rare to find someone who doesn't believe to have seen or interacted with some sort of supernatural phenomena.
The emergence of humanism did jack squat to these people.
About the religion thing, needless to say religions often clash in real life, but there's no reason for say a Christian, after having seen Odin's horse Sleipnir, to deny its existence just because it's part of a different religious tradition.
lol do you even Christianity?
When I say "denial" I don't always mean "the individual completelly refuses X exists". I also mean "the individual interprets that as another thing that better fits what they already believe". So, in a Christian's case: He can see Sleipnir and accept it exists.... But not as Odin's horse, but as an illusion of Satan or a demon from Hell. So, instead of starting to believe that Odin (or at least his horse) is real, this hypothetical Christian will return to his church, share what he saw with his brothers and sisters, and that will become the story of "Joe who saw a demon horse with eight legs" and not of "Joe who saw Sleipnir and found evidence Odin is maybe real".
Risking the biggest fedora-tipping this forum has ever saw: The biggest religions' bread and butter is saying that "that other god/spirit over there" is not real. No matter what you see, it's a lie made up by [respective religion final boss] to make you stray from god's teachings -- the only reality is what their respective holy scripture says. The Bible itself classifies many other gods as demons, for instance.
And in the CV universe that does not seem to be that much different, either... I doubt Juste Belmont ceased to be a Christian after verifying for a fact that Asura and Garuda are real, or Richter ceased to be Christian after verifying for a fact that four chinese animal gods can make you indestructible. How do they both rationalize these phenomena when their belief system says that those shouldn't exist? Hell, in the CV world there is an entire INSTITUTION founded on precepts saying that much of what they see shouldn't even exist.
That might be a viable short-term strategy but once the number of such reports would rise it would become more and more suspicious when these keep being discreted.
These people are called, on our world, conspiracy theorists. Some conspiracies have thousands of followers -- does nothing to change the status quo. It's obvious that there are many who know the supernatural is real in the CV world -- this would still not be enough to convince others. You might argue that, different from our world, in the CV world you can actually gather evidence, but I raise you this: The theorists of OUR world also have "evidence". What do we do at this evidence? We ignore it.
I think it's fair to say that, in real life, the reason most paranormal happenings are dismissed as insane ramblings or products of flimsy research is because they are insane ramblings or products of flimsy research. I would imagine this isn't the case in an universe in which the supernatural is very much real.
Except that our world is full of people who will promise you and
give their life to prove that the supernatural is real. As I said above, they will bring you evidence that, in their heads, proves their claim beyond a doubt and we will STILL dismiss it.
Consider this: On our world, depending where you live, there is a pretty good chance that you'll be called a madman for believing Climate Change or Evolution, but will receive praise for making some outlandish religious claim ("my amputee son went to the church yesterday and regrew his arm because MIRACLE"). Despite the first being VERY well researched and pretty much beyond the stage of "debate", this is the one who will earn you distrustful glares, not the religious claim.
It's all a matter of "who controls the narrative?", and we know that in the CV world the Church (and the government, after a certain period) do.
Also, never underestimate the power of misinformation tactics.