Its not a concrete conclusion at all, it is the refusal to accept the existence of a god given the current facts at hand. Atheism is not the belief in the non-existence (or at least his supremacy and the sway of organized religion) of god, it is a position and a statement. A statement that since no man can conclusively prove that god exists ergo given that fact I chose not to believe in his existence as long as said proof or approximation of said proof is not provided. It is a stand which is open to alteration, there is by its very nature an acceptance of the accompanying fact that man also cannot prove that god doesn't exist ergo one should not go about striking at any and all belief systems willy nilly and that one's stand can be proven wrong and if and when that happens then one shall have to accept that he/she was wrong. It is this very flexibility and the fact that the atheist position must be based on fact as is known so far rather than faith (which is in its real sense belief even where belief would not be merited on any logical basis, not that that in itself is wrong) is what makes it anything but a belief system. An atheist, if granted a visitation by god or having witnessed a "miracle" which he perceives to truly be a miracle (in its exact nature as per semantics) will have to revise his position, something that a believer would never do since his/her faith extends beyond either reason or just personal perception (which has a particular beauty of its own).
