Finish the line: If religion never existed...
Here is mine:
all businesses would be open on Sunday.
I don't think we would have survived as long as we have as a species. Evolution is a machine that throws the old models in the trash and constantly searches for new variations. It landed on very intelligent monkey, so smart it became aware of it's own mortality, and it was terrified by it because it had the drive to survive and protect it's young, just like every other organism that came before. In order for it to function it had to take it's eyes off it's terror and go hunt and gather food. So some especially clever monkeys constructed a tool they could sell and fill that void. We call it religion. And I stand by the conclusion that we couldn't have survived without it, the truth remains that now it's a cancer that is killing us. We are a failed experiment, and the sad thing is that evolution is a random tool, not very efficient. So the next time it lands on something like us, the sun may be going cold.
Well, isn't that a pretty simple question... maybe not.
We know that Religion, definitely not Christianity, was the hub of activity in the first known settlements of people. Perhaps they got together for trade or other reasons but religion left a mark. It left buildings, statues and monuments. They built temples and people came from great distances (for the time) to visit these religious settlements. One could be said that religion was a driver for social activity in early mankind. What would have happened if it didn't occur? We might have developed civilization very differently. Was it religion that inspired war? Probably not. We are too aggressive by our own nature and war is part of a tribal survival technique. We surely would have different reasons for war. Perhaps, we would still be fighting tribal wars where we only would side with our own tribe. Never finding common ground outside of our tribe that religion could give us.
Maybe we're nearly at the same point but we got here differently. At first, developing slowly because of our diversity but without the chains of religion we grow exponentially. War slowly getting eliminated and in order to provide security we group together. No Dark Ages. Logic providing a basis for fighting famine and plague. We might be in a better position to move forward but essentially at the same place.
"...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]