Splunge, it sounds like you're talking about fundamentalist religion.
For example: Here's the text of the religion. Early on you learn that God dictated every word of the text so it's inerrant and infallible, and all you have to do is read it and memorise it. Plain as day. Who could doubt it? And you know it's true, because it says it's true right there in the book. Now, you can stop there, but the results tend to be pretty ugly, both for your own mind, and for the way you act in the world. You ossify. And there are plenty of examples of that around.
So let me ask you this: You belong to the religion. When you go to school, or to a tutor, or whatever, you find out that it's pretty unlikely God dictated the text word-for-word. It was sewn together from sacred myths, oral traditions, customs, and folk-tales, and eventually written down and codified by a number of different people. And if you don't speak the language the text was written in originally, chances are its gone through a few translations as well, and maybe this bit got cut off, and that bit got added in just a little, and maybe this part isn't so original, and it sure sounds like that other religion wrote about it, too, and on and on.
Then you learn about some of the history of your religion, and hey - not everyone was a saint. There were bad people who claimed it, too.
The text is still the same, mind, you just know more about it now, where it came from, what people have done with it over the centuries.
Does knowing more about the text invalidate the text? Does it invalidate the religion? Does it make the good things in it less good? Does wrestling with it, and trying to understand what the people who wrote it down were attempting to convey weaken your faith? Do you walk away entirely because the people who wrote it could only convey the meanings in stories instead of, say, physics formulas? Does it become untrue because it isn't entirely factual, or proveable?
Or does it deepen your respect for the people who tried to communicate these revelations to you from so long ago? Do you understand it better now? Are you able to look at it in a more mature light, and not feel like you were lied to, or misled by it? Does it have even more merit now that you realise you can spend your whole life engaged with it on a much deeper level? That there are ambiguities to be considered, that it's not all black-and-white like you learned when you were little? Kind of like real life is now. And maybe, just maybe, it's that path you need to take that leads to communion with the divine.
I think that's what you're asking about tarot. Could be wrong here, but it sounds that way. And you have to admit, tarot's history has been plenty colourful enough to fit the model.