Your view of religion is decidedly modern - and wrong, at least as it applies to pre-literate cultures. Not all sacrificial rituals are heroic.

Pre-literate peoples lived close to death. They experienced death much more intimately and much more frequently than we moderns are used to. Most believed not only in deities and an afterlife, but in ghosts and unseen forces in the world around them. To them, someone's death was less a matter of an ending than a changing of forms, a transition to a world they couldn't see but were certain existed. The only "heroism" implicit in a willing sacrifice was the fact that the sacrifice was willing to surrender the things of life in order to take his place early in the spiritual world - and when you consider that the things of life included not only such niceties as sex and tasty food but also such unpleasantness as sickness, hunger, temperature extremes, and physical violence, the trade-off (for the volunteer) tended to be viewed as an even exchange at worst.

Further, early religion had little or nothing to do with "cultural manipulation". That is a later phenomenon that came out of the growth of human communities beyond tribe-village size. Frankly, before that point if you wanted to engage in "cultural manipulation", say to bend that oddball character into line or to steer the tribe in toward some desired goal, you did it the the same way the PTA or your local Waterbuffalo club do it now: gossip, relationship networks, that kind of thing. Religion, for pre-literate peoples, was their effort to try to understand and control the world around them.