Some deny that atheism is a belief.
By common sense, and the ability to just see with your own two eyes, this statement is refuted. I walk into the bookstore and head to my favourite sections: religion, atheism, philosophy. I will see a pile of atheist books, oh but wait! These books are nothing, according to some atheists, but some author’s writing on the “lack of a belief” in God. That doesn’t make sense, I wouldn’t write a book on my “lack of belief” in unicorns, I write a book because I believe unicorns don’t exist, and I provide arguments to back that up.
It is also obvious that in these atheist books, and in their debates, they make arguments that they “believe” (big emphasis) prove that God does not exist, or that he likely does not exist.
It’s kind of like saying I don’t have any beliefs myself even though I believe your belief is wrong. It falls foul to the law of self-contradiction.