No the fear thing is probably an evolutionary benefit and a pretty devastating psycho-social drawback.
By the way, the ancestor that was worshiped is the "big guy." "Ancestors" can be pretty expensive responsibilities (both emotionally and financially).
Group-unifying mechanisms are based in human emotions. That is, it is pretty hard to compel human groups to action through logic and really amazingly easy to compel them to action through roused feeling. The most compelling emotions tend to be lust, love, terror and guilt.
I agree that religion has been a primary tool for group cohesion. How it actually functions in society is by manipulating the emotions of individual humans and our basic social primate nature. One of those "basics" is our need to obey authority (the consequences of refusal can be grave for both individual and group if in a moment of crisis someone stops running away and says "Hey wait a minute, is that jackal really meaning to eat me?" So we have an inbuilt need to obey, to fear disobedience, and an absolute terror of being abandoned and ostracized. Of course that has its downside. The Milgram experiments show us the downside in a secular sense just as religious wars show us the same thing is a non-secular sense.

