As to your last tension, atheism is based not upon the belief in no god but in the lack of belief in one.
Is it though? The definition of atheism seems to vary, going from the disbelief of the existance of any deity to the belief that there is no deity. What I gather atheism as a whole encompasses both ideas, and in my experience it is usually equated to positive atheism. I suppose the question is open to interpretation as to wether it refers to positive or negative atheism.
Evangelists like to mess with the term to make it easier to refute. Atheism derives from the following rationale:
The explanation which requires the fewest assumptions is the most likely to be correct (Occam's Razor). Since we cannot know something is true with absolute certainty (excepting certain constructs which are necessarily true, or at least assumed to be necessarily true to avoid absurdity, such as the principles of mathematics and logic), due to the fallibility of the senses, the most likely explanation is assumed to be correct until it is disproved. The explanation of a supernatural creator has no evidence (we live in and work with the natural world, and the supernatural - a suspension of the natural laws of the universe - is scientifically unprovable; the unfalsifiability of religion is central to its perpetuation) and there is no phenomenon which necessitates its existence. Therefore, it is unreasonable to assume a creator when there is any natural explanation. Further, for any phenomenon that does not yet have a natural explanation, it can be assumed that one will be found, because all phenomena yet found have had a natural explanation. In short, there is no need to assume a supernatural creator, so it can be said with reasonable certainty that there is none.
The idea of atheism as a positive claim simply comes from lingual acrobatics. The conclusion that there is no deity because no reason has been found to suggest there is follows the same logic as the conclusion that there are no fairies because no reason has been found to suggest fairies exist.
By the way, if this topic is going to continue it should probably be moved to its own thread, at the discretion of the OP.