Most of us are atheists. As doubters of religious doctrine, freethinkers generally are atheists or agnostics. Most, of the SSA's members disbelieve in or doubt the existence of a deity.
However, skepticism of religious dogma is only a part of what defines the SSA. Among other things, supporters of the SSA believe in religious liberty; church/state separation; the humanistic notions of equal rights and the inherent dignity of every human being; the importance of science and critical thinking; and the importance of caring for humanity as a whole in the absence of Divine guidance.