Ever watch South Park? There's a episode where atheism is declared worldwide, and religion no longer exists. Cartman (the fat kid) travels to the future, and several atheist factions are fighting each other because of their different scientific beliefs. People will still be different from one another regardless of the absence of religion, and usually, as history has taught us, blood will be spilled over those very differences.
I agree. Religious wars, and wars being waged over beliefs, are grim and ignorant. But until we learn to accept those beliefs (regardless of how ridiculous and false they are) can we live in peace.
"Peace cannot be achieved by force. It can only be achieved by understanding," ~Albert Einstein
Later in the episode, the future gives up on all the "isms" and humanity is still at war. (this time over land)
Technology will also perish, like you said. I cant believe people who deny science.
Humanity wont die from a religious war. Humanity (Or at least civilization) will perish from the next ice age (cause by global warming, our fault, and there are still those who deny it), which people who were convinced that a certain character named "jesus" would not allow such a thing to happen.
But I'm pretty positive blood will be spilled until that time from religious wars. War shows that humanity is imperfect, along with this world. My anti-war views don't seem to change a thing. Humanity cant come up with a better way to solve problems.