The need for some to force their beliefs on other people is the cause of so many problems. That is all about power, as I see it.
The biggest mistakes, though, were agriculture, and cities - but that is another story.
I am currently reading a book about medieval England, and boy did they need Gods to get by! For 90% of the population life was unbeliveable hard, and few lived to be very old.
It is easy enough to reject gods if you are not directly depending on things beyond your control, like farmers, sailors, soldiers etc. But I think most of us tend to pray or have mascots for charms in such situations - circumstances beyond our control. Even atheists.