You talk about Atheism as if it is a religion itself. Do you really see it that way? Unfortunately the thing is that the word Atheism itself is religious oriented since it defines the lack of beleaving in God. But if there is no God then is it not wrong to base a definition upon something imaginary! In my opinion no atheists exist, only theists.
There are many ways to define atheism without using the word “god.” For example, an atheist is a person who is without religion or a person who is not a theist.
I also disagree with the statement that it is wrong to base a definition on something imaginary. In fact, from my perspective, “religion” is defined in just this way.