Its quite possible that atheists belong to the ToS. By their own literature we can see that it is unnecessary to hold a theistic belief in Set to be a member. Though I find it hard to believe that an atheist would stick around for long, I think that at any given time there has, is, or will be atheists who join out of curiosity.
A more specific question is how does the ToS define theism?
The organization was started by ex-members of the Church of Satan so lets begin our investigation with it.
If man needs such a god and recognizes that god, then he is worshipping an entity that a human being invented. Therefore, HE IS WORSHIPPING BY PROXY THE MAN THAT INVENTED GOD. Is it not more sensible to worship a god that he, himself, has created, in accordance with his own emotional needs--one that best represents the very carnal and physical being that has the idea-power to invent a god in the first place?
-Anton LaVey, (The Satanic Bible).
If, as Aquino asserts, the founding members of the ToS resigned from the CoS due to the selling of degrees, is it probable that they all suddenly had an epiphany of the actual existence of some great cosmic ant-eater? Not likely, so lets look at the above quote again.
Prior to the Church of Satan, Satan was defined by Christianity. It was the formation of the CoS that provided its membership the ability to publicly define Satan as a cultural icon that represents The Nine Satanic Statements. So the CoS essentially hijacked the Christian devil to promote a religion based on carnality. If someone then chooses to worship this icon, they are worshipping by proxy, those that define the icon (Anton LaVey and his priesthood).
So I ask again, is it probable that ex-members of the CoS, who prior to their disgruntled exits were representatives of the Satanic icon, suddenly became theists? Or, is it more likely that they formed the ToS in imitation of their predecessor? Only this time, rather than have one person who stands out as Set, the entire priesthood will embody the Set icon equally.
Just as the II* represents the height of personal identity, and glory to be taken in that identity via application of the Black Arts, so the Priesthood involves the opening of a very special kind of door: the merging of the consciousness, indeed the personality, with that of the Prince of Darkness himself
.
-Michael Aquino (Black Magic in Theory and Practice).
Hence the Priest or Priestess when acting as such, for Priesthood is a deliberate act, not an office is something more than human, something more than the individual whose human visage appears before onlookers. At such times he or she is not possessed, but is rather become a veritable living Temple indwelled by the presence of Set.
-ibid
Isnt this just a fancy way of saying that Set is the priesthood of the ToS?
And do those who believe in the priesthood, believe in Set?
We suggest that subjective realities do objectively exist, as indicated by their affects upon the objective reality.
-Robert Menschel (Ruby Tablet of Set)
Ah, I see, so whatever we imagine, actually exists once we draw a picture of it. And since Set is a figment of the imagination that someone wrote a poem about, then Set exists. I wonder what the unicorns make of all this