Religions and social evolution

Premise nr 1: Religions are but a sedative; nothing else. They help us to bear life and, eventually, to face death. In this way, they act like painkillers, dumbing our mind, and even our senses in some cases.
This is why all religions involve some way or other of continuity along the existence beyond death. It’s easier to accept death knowing that our soul, energy, spirit or whatever, are millionaires in eternity.
This is well known.
Premise nr 2: Also, it’s an obvious fact that religions are evolutionally advantageous. More than a fact, this is actually a tautology. I can’t comprehend the means by which religions are beneficial to human nations, but they must needs be: otherwise, they wouldn’t have survived to this day. (I’m talking, of course, about social, not genetic, evolution.) So, there has to be some advantage for a people in the fact of their individuals being religious; but which advantage this is, I know not.
Now my only doubt is, when connecting the above premises, how come that atheists have not taken over the nations? Because an atheist knows he will not live forever, a stronger drive for remaining alive can reasonably be presumed in him, thus having more chances to survive and disseminate his beliefs (in the same way he’d spread his genes). For the same reason, suicide would be expected to occur more often among believers, as atheists “have more to lose”. So, why atheists have not overtaken the human populations?
Or is it that, despite being spiritually perennial, the drive for accomplishing their “mission” gives an advantage to believers comparatively stronger than that of atheists?
Please comment if you know the answer to this, or recommend me some lectures on the role of religion on social evolution.