I have done a lot of research on this in recent months. There is no evidence that a god exists. No being has ever stepped in to rescue us from one another or to change the trajectories of the worst we can do. I couldn't understand why evolution would screw us into believing in illusions. I was and still am quite hurt by it.
Gautama Buddha said that gods exist but do not engage with us or intervene in our lives. But he often said conflicting things. He said that he had been Brahma in a previous incarnation, and that when he attained what he called perfect enlightenment, Brahma approached him and convinced him to share his teachings because there existed those who had little dust in their eyes and were ready to attain enlightenment.
I've read that a benefit of believing in a god helps self-regulation of emotions. Many religions view god as a parental figure, and there have been studies (I do not have the sources) that show the same areas of the brain that relate to parental attachment activate in response to one's belief in god.
This makes sense when I consider that "God" seems to justify people doing horrible things to each other. It is higher support for or rejection of certain actions, much like getting encouragement or discipline from a parent. It provides a way for cultures to regulate the social aspects of interdependent beings, such as the ten commandments, the five precepts of Buddhism and Jainism (spiritual but not religious pursuits).
We are also both blessed and screwed by the evolution of our brains that created language. Language is symbolic. The word represents the thing but is not the thing, and relating to the OP's comment about culture, "God" varies from culture to culture. When I hear the word "tree," I have the internal referent of an oak tree; someone on a different continent would think of an entirely different type of tree when they hear the word. But we could agree in a general sense about the word-symbol "tree," and all cultures can agree on the concept of a god as being non-human and having powers that humans do not. Based on that description, we reach out to something that has greater power as we do to a parent when we are young. In some cultures, there are multiple gods and demons which represent the best and worst of human qualities. Ultimately, I think gods and devils are us, and represent what seek to attain or to destroy. Religious rituals create social cohesion and stimulate the hormone production that instigates and maintains bonding.
With symbols, we create meaning so we can manage uncertainty in a world we do not always understand. We rely on representation and creating meaning. Language serves us as social animals who are interdependent as a means of survival, and language only works if we agree upon the meaning of the symbols used. We may hear a noise and attribute it to something supernatural and scary until we learn the source, which serves our survival even if we believed in the imaginary. Trying to figure out what we don't understand and to solve problems propels pursuits of invention, philosophy, and spirituality so that we can attain more safety, certainty, and comfort. The concept of god provides safety, certainty and comfort until we know more. The more we follow the pursuits to attain these things, the more our entire species evolves, and the more the brain grows, such as the discoveries and creations of tools like fire, the wheel, creating weapons from stone, iron, and steel. We always have to protect ourselves from the elements and from others outside of our tribes. And we grow because of adversity. Stress is a requirement for adaption so that a species can survive and thrive.
So as I write, I come to some conclusions.
1) Yeah, we're fucked. I don't see how peace and world unity would fit into evolution as there is a striving in species to take over as much as they can, and limits to how many people a culture or social structure can include. Humans love, but humans also fight, are tribal, and I don't think evolution would allow that to change.
2) We are both inspired and manipulated by the symbol of "God." We do more than we are capable of because of it, and we are inhibited in reaching our potential because of it (cf. religions that give men power over women even though women are equally intelligent and capable, and often more so).
3) Religious dictates are often revelations of how humans must biologically function as social beings, and can often be simultaneously found in philosophy, such as the golden rule which is found in some form in every religion and in many schools of philosophy, such as the reciprocity found in confucianism. In the search to understand and eliminate suffering, both Buddhism and Stoicism advocate non-attachment.
4) Based on all this, I cannot reject the possibility of gods or higher beings. Such beings do not seem to benefit me as an individual, yet the striving for a connection to something higher has benefitted our species by providing the sparks for great progression, as well as retardation of achieving potential and justifying the unjust. Yet we persist in believing and striving to reach. It is an adaptive trait that serves in many ways to support us, bond us, and justify us. So I remain open, but I am also very hurt and offended by biology, evolution, and god.
5) Traits are never fully discarded when they no longer serve a species. Whales returned to the ocean yet still have some leg bones in their fins. Humans have a tail bone. Some people have a little vestigial gill that appears as a hole next to the ear. So if we stop as a species believing in and seeking god, as atheists do, then I would imagine this adaptive trait, no longer needed, would shrink and remain dormant in case it is ever needed again. Perhaps there is a god in everything that seeks some perfection we don't yet know. That tells me that God is not love. That may be one of God's traits, but there must be many, many others. It also indicates to me that if there is a being, God, then that being evolves as well.
Thanks to the OP for starting this thread and providing a space for me to work through this some more.
