I've been thinking about this lately. Old-world religions like those of the Greeks, the Romans, the Egyptians, etc. are all dismissed as myth and folklore, so how is modern religion any different? Why are Christianity, Islam, Hinduism, Judaism, etc. all considered to be legitimate bodies of faith while those of the past are dismissed? It just seems like selective logic to me - "Oh, those people were uneducated pagans. But I got the right god, don't worry!"
Add to this the fact that all of the religions of the world are based on the writings of long-dead men who thought that the earth was flat. How can the religious possibly proclaim that their faith is true and valid, while simultaneously condemning the others as baseless?
Maybe it's because nobody worships the "old" religions anymore, so they must not be the right ones. But don't worry, we'll find the keeper!