Oh, it's definitely something you can get from your upbringing, but atheism is not a religion--it's a lack thereof. Atheism has no formal tenets, no supernatural beings or concepts, no sacred narratives. I'll buy religious "position," but only in the sense that it's outside of religion.

And hell, I do think it's the most sensible idea, because I subscribe to it!--but I ain't gonna tell others what to believe.