I don't doubt that, if the altercations did not change the way secular government and society function, we would still find ways and reasons to kill each other. But, to me, the idea of eternal life in a place unlike earth, where "souls" somehow find a way to pass the time for the rest of eternity seems a bit of a stretch at best to me, so it seems entirely possible to me that if religion was reintroduced at all it could end up as something that would edge people on to kill each other a lot less, maybe if eternal salvation did not hang in the balance.
But like I said, a fear of death is natural. It was not introduced by religion; religion is a *solution* to it. Yeah the details (souls, angels, "heaven" as we envision it, etc.) might very well differ. But the concept of an afterlife? That idea long predates "organized religion", especially as we know it. And I can see why: what an appealing thought, that we can live on forever with all of our passed family, friends, and loved ones in eternal happiness!
I think ethics, however, would develop completely differently. There are so many points of reference where our ethics could branch out depending on religion. You have to remember that, while we've installed all of our ethics as derivative from our own thoughts, most of them were derived based on religion, so any presumptions about how ethics could end up could easily be turned inside out by that fact. As I said, there's no measure to where we end up, worse or better, with out it, but I wouldn't doubt the huge amount of influence religion has had on ethics and acts and the way the world has turned out in general.
Sure, yours and my ethics are partially shaped by religion and what we've been exposed to. But how did those ethical ideas come about initially? Judeo-Christian ethics were influenced by ideas, societies, philosophers, etc. that came before them. And what about codes of ethics that developed relatively independently of the same influences, like some of the major eastern religions?
I think the *basic* guidelines for morals or ethics ultimately come from what we decide we think is best for humanity, and what we learn increases our survival and quality of life along the way.
-J