Religion didn't always serve the same purpose that it does in today's society. Once upon a time, it wasn't "religion vs science", because both were one in the same. Religion is a hyper-primitive form of proto-science. It was used to explain the stars, moon, sun, tide, seasons, life, death, creation... Just in ways that egyptian cave monkeys could understand.
Was it all wrong? Well, yeah. But we have to remember that religion did have a structure to how things worked within it. There were rules hat governed how the world worked. It just turns out these rules were woefully uninformed. When man began to properly answer more and more questions that religion could not, these answers were applied to things that religion had already explained. The result was the dark ages, where scientific thought not in support of God's existence was punishable by death. It wasn't until the Renaissance when man lifted the veil of religion to find true scientific thought behind it.
So where would man be if not for religion? In caves.
Where will man be if we refuse to give it up? At war.