Atheism could be better and more helpfully known as Egotism. Why? Because firstly in relation to the living reality of consciousness, atheism is more or less a totally abstract term. Abstract as where does it as an experienced reality exist within this consciousness? By constantly reminding oneself of the non-existence of something one isn't in that moment or any other moment by definition experiencing! Were it to attempt to be not abstract but practically relevant to moment-by-moment existence, it would esentially amount to the running commentary of a stupid malignant dwarf imposing itself on experience by continually reminding the experiencer of the 'rational emptiness' of all experience - telling him not to be carried away with the experiences as they are all accidental. Whereas existentialism should imply a naked non-judgemental openness to being, atheism is an anti-existentialism where this reality as a whole is judged negatively as meaningless, accidental, etc and so given one is imposing this filter upon reality, reality is never experienced existentially - as long as one is an active moment-by-moment atheist. For example, one is sat in a garden on a beautiful day. In what sense can one be an atheist here.
"God doesn't exist."
"This is all accidental."
"Why don't you just sit back and shut up and soak it in?"
"You're just deluding yourself. What's there to soak in?"
Someone might say actively believing in God is equally anti-existential; that one is again imposing a filter of the mind upon reality, and so one is not in an internal 'open' position to experience reality . This may be the case if someone gets too intellectual about what faith implies or involves, their thought processes taking too active and dictatorial a role in deciding what's what. However this shouldn't necessarily follow at all, and instead a belief or acceptance of God can simply entail or coincide with a necessary intellectual humility to accept reality and one's seamless part in it, without the need to impose a spurious judgement on it.
That's not the point that set this piece in motion though so back to Egotism being a more apt meaningful term for Atheism which as said has only meaning by inference, and in itself seems to be an irrelevance or evokes nothing in terms of a philosophy of being or awareness. That it should be much more vividly termed Egotism may evoke a knee-jerk emotional response as to its unfairness, but it's easily enough shown to be fully justified.
So atheism is essentially a philosophy of Egotism because it is the belief that ego is the highest reality, that there is nothing beyond - both in the external sense of there being no God, and also in an internal sense in that there is declared nothing beyond in the sense of consiousness; that consciousness has its limit in this self-sustaining language state of egohood. It is in such an environment the pinnacle of existence, the core of the highest entity of creation. So atheism is the intellectual manifestation of the ego, itself distilled. And naturally enough within this idealism of the ego, these isolated centres of consciousness, the more pure the isolation and selfishness the more pure the truth. This is the implication of its 'truth', all divided against all, each ego seeking supremacy - as otherwise that individual ego has failed to be the pinnacle of existence - and inevitably if pushed to a conclusion such a philosophy, if let run its unimpeded course, leading to total self-annihilation as even if one ego prevailed against all others, its hatred would finally having no external targets to aim at, be forced to face and turn on itself.