Phizzy, I found the definition here: http://atheistempire.com/atheism/atheism.php
It´s possible that Atheism and Religionism can, as you write, be like two opposing teams, just like black and white, yin and yang etc. Separated but maybe connected anyway. My limited experience with people from both sides, they have a lot in common; both are confident in their point of view, both think they "know", both claim that they have right and others with diffrerent point of views are wrong etc etc. If my understanding is correct, arrogance and pride have these features too.....