from "A Brief Guide to Alcoholics Anonymous: What is A.A.?"
It was in that time in history that A.A. was created.
In 1934, Bill Wilson was hospitalized, suffering once again from acute alcohol withdrawal (which is often accompanied by hallucinations and delusions). He was also being treated with belladonna (a known hallucinogen in its own right). It was under these conditions that Bill had his now-legendary "white light" experience.
It's interesting to note that one of the first A.A. members was Jim B. He was a self-described "militant agnostic." After an early relapse, he remained sober and outlived the two founders of A.A. Jim started meetings in Philadelphia, Baltimore and San Diego. His story was even included in the First Edition of the book, "Alcoholics Anonymous," the book generally referred to by A.A. members as "The Big Book." Some of his story can be found here: Sober for Thirty Years.
A few things have changed since those early days. Our understanding of medicine and science and public health and sanitation has grown exponentially. One might expect that even A.A. itself would have matured and grown and advanced during that time, and in many important ways that it has. It has certainly expanded its thinking with respect to the participation of women, racial minorities, and those of non-Christian faith. A.A. now has meetings which exclusively serve the LGBT community, women-only meetings, men-only meetings, meditation-based meetings, and meetings for young people. It's time that A.A. expand itself once again to more actively include and support those members who might not have a belief in things which exist outside of nature, or for whom "god" is not a reality.
And, “...the A.A. program of recovery is based on certain spiritual values. Individual members are free to interpret these values as they think best, or not to think about them at all.”