What defines us as athiests is that we reject the concept of a Deity. We assume this posture by using logic and reason. A deity is logically extremely improbable. We then go on to rely on logic and reason to construct our cosmology based on observation, scientific inquirey, rational deduction and so on. We each have a belief system on which our sense of the world is constructed, our reality so to speak.
I've been reading a bit about quantum mechanics and multi universe theories. None of this fits neatly into my cosmology. Even so, the theories are reached by logic that I can follow and can't really dispute at my level of understanding.
To approach concepts like the nature of our consciousness reveals the limits of logic and reason. Logic and reason would ascribe them to chemical reactions in the brain that interperate stimuli. But we only have five senses with which to evaluate the world (if an external world actually does exist!). Is it not reasonable to assume that there are things imperceptable to these five senses? If consciousness is indeed a chemical function of the brain, then we rely on the eyes, the ears, the nose, the skin to give us all the interaction with the physical world and supply all the data that the mind asesses. Can we trust that these mechanism are supplying accurate interperatations of the physical world?
And what's going on in the next person's head? Are we sure it's similar to what's going on in our own? Is each person a unique universe? Do they really connect in a physical space? One of the theories is that all matter is a congealing of possibilities enacted by consciousness, that in fact the universe does not exist on it's own without consciousness to define it. This begs the question, do any of you exist outside my head?
What I'm getting at is that religion provides a rudimentary construct for us to understand and relate to the universe. I believe our logical, reasonable, scientific cosmology is no less an invention of our mind than religion and is dependent on your intelligence level, understanding of science and philosophy, life experience, indoctrination to other cosmologies, level of inquirey, and psychological makeup among many other factors.
Who are we to be so disdainful of religion when our concept of reality is no less an invention of our minds? Is it essential to the human condition to have a cosmology? If it is, doesn't religion provide an essential construct for some?
Everything is all in your head. That doesn't make it any less real.
We do make a few assumptions, for instance, we assume that it is possible to make sense out of the universe. But reality appears to be completely consistent with our assumptions, and with itself. I may exist only in your mind, but that doesn't really matter.
There is no difference between a perfect illusion and reality. I feel solid keys under my finger as I type, I believe them to be real, but would my life be any different if the keys were not solid, but my mind did such a thorough job of convincing me that they were that it was completely impossible for me to tell? You could conceivably be a brain in a vat, with stimulus put in to simulate what we experience. Or you could be a complete lunatic who has constructed a false reality to live in. It doesn't matter though, because our apparent reality is consistent and inescapable, at least for the moment.
Religion is quite different. We have an experience, and try to learn what we can from it and enjoy it. They have an experience, and believe explanation that does not at all fit the observations.
A relevant video on the topic: