Premise 1: If God does not exist, then something like Blind Watchmaker Neo-Darwinian Evolution (hereafter just “evolution”) is a fact.
Premise 2: If evolution is a fact, then, objectively, my only purpose in life is to survive, reproduce, and spread my genes to the maximal extent (this premise is taken, essentially, from the mouth of Richard Dawkins).
Premise 3: Belief in God brings about the most health, happiness, and fecundity (after all, orthodox believers are much more fruitful than secular atheists).
Premise 4: Being healthy, happier, and more fecund increases my ability to survive, reproduce, and spread my genes.
Conclusion: Therefore, I should believe in God rather than not.