Of course atheism is operationally a religion.
My point was that if atheism is recognized as a religion, atheist harassment of traditional religions can be considered an effort to favor one religion over another. The atheist demand to scrub Christian (and other religious) symbols and memorials from the public square will become a de facto attempt to institutionalize a new state religion. Modern atheism in the political and legal arena has gotten traction by attacking “religion” as a prohibited category. Atheists can’t do that if atheism itself is a religion.