Finish the line: If religion never existed...
Here is mine:
all businesses would be open on Sunday.
"...the world would live as one"?
A great sentiment but I find it improbable. Humans, among their many varied traits, can be altruistic through nihilistic; not only as a race but exhibited by most individuals, often within a span of minutes.
I'd like to think we'd be kinder to each other and the environment. Also that we'd strive for greater understanding and achievements.
Sadly, if we didn't have religion to wage war over I'm sure we'd find something else. Like power. Wealth. Oil. The true "holiest of holies".
humanity would never have made any advances, as before science, the men in silly hats helped focus our collective energies for the greater good. Now science has taken over hopefully it will operate for the greater good rather than stone cold logic [in which it could see the lack of use for homo sapiens on earth]