I think this really drives home my point - a sect split off from judaism (a religion which very much DOES believe in the afterlife) and within a few generations went extinct again. Moral of the tale: No belief in afterlife = not a viable religious belief system.

Post hoc ergo propter hoc. You have to examine the full story of that extinction and others like (and unlike) it before you can make this assertion in confidence.

Susceptibility to beliefs which fit a fairly specific list of criteria may be HARD CODED into the average human brain.

The more specific the list, the less credence one should give it. Evolution will build just enough structure to let environment provide the rest of the information.

Religion is only one source of group cohesiveness conveyed by deeper meaning. The other major one I can think of off the top of my head is nationalism. The role of ritual would probably be best understood by examining it in all of the contexts where some deeper meaning is the binding agent, not just religion. Military rituals would be a good place to start.