From a diachronic point of view, any concept must come into existence, that is, it must not have existed at some point in the passage of time.
The argument for God and existence of God supposes and privileges eternity and presence. Theism, then, supposes permanence. This must necessarily extend to atheism. Thus the idea of atheism must have been there from the beginning.
The theists have therefore pulled wool over your eyes when they argue in this way. The only way out is to argue for finitude, absence and impermanence.