The christian says that he can prove the existance of God if I have faith. Faith is defined in the bible as; "the evidence of things not seen". In other words; I must believe that God exists before I can see the evidence for his existance which I needed in the first place to believe in His existance. And around and around the chicken house the monkey chased the weasel etc.
Isn't atheism just as blind? "I fail to see evidence and therefore concretely say there is no God." A lack of evidence that there is no God is not sufficient evidence to conclude that there isn't one. You haven't seen all there is to see because we have discovered barely a fraction of what is available to discover, so how can you say so concretely there is no God?
I'm not saying Christians or any other form of believer is correct in their assumption, I am merely saying that every assumption is simply just an assumption.