I don't think this is really the right way to think about Christianity for many believers. C.S. Lewis says, "I believe in Christianity as I believe that the sun has risen: not only because I see it, but because by it I see everything else." It's not so much that Christianity is just another fact lying out there that we just happened to stumble upon, and now we use scientific tools to investigate whether it's true or false. No - it's a belief that shapes the very way we understand the world. It's a worldview. That's not to say that it's necessarily correct, but just that it's not a belief that we necessarily acquire in the same way we might acquire a belief about what 1+1 is or how many planets orbit the sun. It's much like how someone born and raised atheist doesn't hold their belief in atheism because of some evidence for that view. We can still argue about Christianity, atheism, or other religions, of course, that's fine - but it's not obvious that there's some inherent irrationality in asking "what could show Christianity to be false" instead of "what convinced me Christianity is true".
>they were told from a young age that this was real and just kept believing as they grew up. This is true, but if the implication is that belief in Roman paganism is on just as firm intellectual ground as belief in Christianity, that seems unfair given the rich intellectual history spanning millennia of the latter to which the former isn't really comparable at all.
