But one can hypothesize the possibility of a god or no-god, and argue from this hypothetical base. But one cannot argue the philosophy of life, universe, morality, and more with the pre-existence of an absolute belief one way or the other.
Let me argue morality from the atheistic point of view. Is a moral and ethical code possible without a central belief in a supernatural power? Of course. One can advocate the principle of social Darwinism - that our ethical and moral codes can stem from our needs as human animals to survive as a group, as is the case for many other animal forms who have learned that within their herds or flocks, etc. there are social rules to be followed. Our ethics, morals, and laws can originate from such needs, as can our needs to "explain" what we otherwise cannot explain.
Gods exist to "explain" what we "cannot explain." The belief in a god helps assuage these needs, particularly our strong need to imbue our bodies with the concept of an everlasting spirit that will continue to exist beyond our deaths, or that will, at some distant point in time be resurrected into a living form. Human society also needs gods to form the idea of absolute good, as well as the concept of absolute evil. These, of course, are concepts which do not, and never have existed. But a future "heaven on earth," represented by the presence of absolute good and the absence of absolute evil, has always been the everlasting unachievable desire.
I am a non-believer, but, that said, I am an ardent supporter of the idea of a god as necessary for a society that exists in the presence of many unknowns. A god provides an ideal for good. A god serves as a concept that helps acknowledge that human thoughts and decisions are not always rational, but emotional as well. A god provides the "missing link" between matter and essence. A god provides strength under duress, and answers where none otherwise exist. God-concepts (religions) have existed, in one form or another, to provide such answers since the beginning of recorded time! I also think that a world without a god-concept would be a rather sterile world; bereft of the very strong human emotion that ties into who we are and what we are. Religion has been a central point of all surviving societies - it clearly seems to be a societal necessity. Religion plays a need in the "public square." It helps punctuate life.
The idea of a god and a heaven provides an everlasting reach for man. But this "reach" which will always exceed man's "grasp" is what helps stimulate us to be the remarkable beings that we are.