I think there are several 'classes' of atheists. For example, those who merely do not believe in any God but go about their daily lives without giving it much thought. (I have a very dear friend who falls into this category.) Then there are those who are quite heated about 'religious' folk and despise all believers. These tend to have a dig when they can in order to make their views stridently known. Then there is the militant category, the 'Fundamentalist Atheists', whose aim is to undermine and overcome all religious activity in society, seeing it as harmful and dangerous. These attack by referring to all the sinister and reprehensible events in the history of Religion (of which there are many!) and writing erudite and well-expressed books, or making interesting TV programmes seeking to discredit any or all religions. I uphold the rights of all these groups to express themselves, and (using legal methods) to attack belief-systems of others. In the broad sense, their Atheism is indeed a religion. But in the narrower, more usual understanding of the word, it cannot be seen as such.