Ah, perhaps. But humanity is a thing of diversity. Our uniqueness of language, culture, and custom gives us a way to express ourselves. If a single world religion became top dog and every person was born and raised in it, there would still be other religions, since some folks would see the presence of a single religion as a bad thing... some people only feel purposeful when they strive against the masses.

The heroic tendency of humanity would ensure religion doesn't stay uniform.

Moses, Luther, Buddha, Muhammad.

Maybe I'm just a little cynical