So in short you claim that statement A 'There is a God' is a belief and statement B 'There is no God' is not a belief? Even if they have the same probability of happening.
It sounds logically contradicting to me.
Statement B is sets up a false pretence in regards to what atheism actually means. "Lack Of Belief" does not equal "Believes Otherwise." The atheist does not assert with absolute verisimilitude that God does not exist, it is indifference to the possibility of a god. The only atheist that would assert the statement "There Is No God" would have to be one that completely denies the possibility of one. Such an atheist would be a Gnostic Atheist. However, since there can be such a person described as an Agnostic Atheist, or one who does not believe, yet admits they cannot be sure, the term Atheism cannot be said to be a belief. Gnostic Atheism can be a belief, Agnostic Atheism cannot be a belief.
As I have said multiple times in this thread, Atheism is not an "-ism" as in it is not something to which one can subscribe to. The suffix "ism" also means a "state, condition, attribute, or quality" like pauperism, astigmatism, heroism, anachronism, or metabolism. Is astigmatism a theory? Is metabolism a doctrine? Is anachronism a practice? Not every word that ends in "ism" is a system of beliefs or an "ism" in the way people usually mean it. The very essence of Atheism
being in a state of non-belief, it is not a subscription to
believing that God does not exist. Atheism is by itself just the absence of belief in gods; it's not even a single belief, much less a body of beliefs.
In this way, a baby is in a state of atheism because it is not actively believing in God. It can have no perception of a god, thus it cannot believe one exists, nor can it believe that one does not exist. Grown adults who have never heard of a god are no different.