What about ancient Aztecs? Incas? Completely isolated from Christianity for a vast majority of their empire's existence (but fucked over due to Cortez and Pizarro) , yet they created their own systems of beliefs with their own gods. To them, it was truth. Think about why their gods were imaginary, then apply those same standards to whichever god you may or may not believe in. Open your eyes, the only difference between religion and a cult is a few million followers.