Among the comments on The Diane Rehm Show for Friday, 15 January 2016, one complains that Derek McGinty, the guest host, had much too quickly dismissed a call for (ultimately) eliminating religion to eliminate terrorism and other bad things. McGinty said the idea was — if I heard right — a "nonstarter."
The commenter was right to resent the offhand dismissal, but McGinty had a point, given the numbers. Atheists are a small demographic, while believers' numbers are massive. The world may be moving toward the secular — and a recent book called Big Gods suggests that there is the possibility of an ethical, post-religious world — but currently the idea of large numbers of people giving up their beliefs and accepting a life of "Emptiness! Emptiness! All is empty" and futile is a nonstarter.
A relatively objective, scientific, realistic assessment of the human condition is that the human species is trivial even in just our universe, to say nothing of a multiverse in which the vanishingly small significance of our galaxy approaches literal nothingness in what may be an infinity of worlds. Statistically normal people want significance for humanity and even individual human lives, and it's difficult to justify such ideas without some sort of leap into the absurd. Believing in God is a leap of faith; beginning that in The Big Picture some individual human is significant is just "counterfactual," what Kurt Vonnegut labels a "foma" in Cat's Cradle (1963): a comforting lie.
Other numbers that need to be looked at are body counts, conveniently tabulated by Matthew White on line and in The Great Big Book Of Horrible Things. Religion (God knows ...) has produced an impressive number of human corpses and other atrocities, with the monotheistic, Abrahamic religions no slouches in slaughter. Still, humans are capable of killing humans in massive numbers for reasons less rationally elegant than religious fanaticism. Simple greed and arrogance led to the small-scale genocides of California Indians during the Gold Rush, and — unless you buy the Christianizing and "Civilizing Mission" bullshit propaganda — the large-scale murder in King Leopold's Congo and other places in colonized Africa. Genghis Khan felt the Mongol form of the Mandate of Heaven, but his conquests with their forty million dead were mostly nitty-gritty political. And, of course, Stalin was officially an atheist and didn't pay a whole lot of attention to spreading the doctrines of the Russian Orthodox Church.
Certainly Idealists and Guys With Theories and Weapons are major threats, especially when they believe that the real human reality is in a soul separable from the body and of infinitely more value than the body. The Theory, though, doesn't have to be specifically religious, just idealistic enough to get fanatical about. Or, as with slave trades and slave economies, millions can suffer or die for other people's profit and joy in power.
It is probably a "foma" to believe that God exists and cares about human life and indirectly gives our lives meaning and purpose. To use an idea from Henrik Ibsen's Wild Duck (1884), that human life has value may be a kind of species "vital lie," or "life-lie": a necessity for survival.
Ara Norenzayan observes in Big Gods that most psychological research has been done on the "weird brains" of people who are "Western, Educated, Industrialized, Rich, and Democratic." That's a minor point for me; the major one is that the great majority of people are not weirdly wired and part of such statistical normality is religious belief. That's about as close as you'll come to an objective fact, and atheists who want the world to "get real" need to deal with that fact. They also need to deal with the implications of a rigorously materialist view of the human condition. The "Emptiness! Emptiness" of Koheleth ("Ecclesiastes") is one starting point for that discussion; so is the rigorous philosophy amid the twisted pornography of the Marquis de Sade in the "Manners" pamphlet — "Yet Another Effort, Frenchmen …" — in Philosophy in the Bedroom (1795). The mad but logical Marquis can argue that murdering someone doesn't really destroy life, on balance, since if you bury the body and dig it up later, what we'd call biomass has, if anything increased; and there's no particular reason in nature — only in humans' bias in favor of humans and human consciousness — to prefer the biomass of a living human to that of the organisms of putrefaction.
Me, I am by temperament a vulgar Pragmatist — I check out where logical premises are going before accepting them — and one who read some Existentialism for Dummies at an impressionable age and took a fair number of courses in the life sciences. I'm also a Vonnegut fan. There's much bracing stuff in Koheleth and de Sade and Vonnegut and Jean-Paul Sartre in simplified translation. Still/So, as a practical matter, I'd prefer it if my fellow humans carefully follow beliefs that hold down body counts; and I'd prefer it if people who see themselves as tough-minded toughed it through the implications of their beliefs.