What is 'God'? The great creative source, origin of everything. "Let there be life" from which everything develops and continues developing. All development is adaptation to the environment for survival. This does not negate a "creator". The planet changes continually and all life must change and adapt or perish. The creation was not a fixed anything, but a great rolling stream that appears to evolve and develop towards consciousness. Like all creators, there's something new every day!
What is this life without a transcendant? We seem to have a built-in recognition and need for something bigger and better than ourselves - something that outlasts us. Humans set themselves up as Gods but rapidly crash. Crowds adore and cheer and then demolish and kill. What meaning does this have if there is no agreed structure to mediate all this flow of need and energy? If the value of human life is reduced to 70 pence worth of chemicals, or to a 400,000 pound house, car, fancy gear, dissatisfaction rules. There is no limit to bigger and more. The hollow at the centre is filled with transient distractions and addiction.
"If we observe the general behaviour of archaic man, we are struck by the following fact: neither the objects of the external world nor human acts... have any autonomous intrinsic value. Objects or acts acquire a value, and in doing so become real, because they participate ... in a reality that transcends them." (Eliade, 1954, Bollingen Foundation). This amounts to 'living by projection' and by myth: assignment of value and meaning coming down from ancestors and gods. The few remaining tribes that still embody these ways are destroyed by our cash-register values.
This does not deny the values of the scientific-materialist world. But science measures and analyses, explains life in chemical and mathematical terms, and assigns values by the cash register. These are supremely useful in creating the cash-register society, but they do not satisfy the spirit. I see no conflict between the spiritual and the scientific, as they address completely different aspects of life: the scientific numbering and dissecting of it, giving explanations of its mechanisms vs.the metaphorical stories that point to the purpose and value of human life.
A belief in a supreme principle gives a feeling of inner solidity, of purpose, and of calm, which measured by brain chemistry is seen to benefit the organism. Living through the heart radiates through the self and others and promotes altruism. Love strengthens and solidifies, but also exposes the lovers to loss and pain. Where does comfort come, in the cash-register world, where loss and pain, and depression, are seen as 'failure'? (In 25 years of bereavement counselling, I could count the believers on the fingers of one hand).
Aetheism - the denial of a supreme principle - is profoundly negative. It denies there is a purpose and value to life, both in Nature and in Humanity. We are all more than the sum of our synapses and chemistry, and life has more value than just fodder for industry and the accumulation of wealth.