I don't think atheism constitutes a religion, but I think the definition of religion is more broad than we believe to be. In theory, a single spiritual belief that is common among X group of people is enough to constitute a religion - Everything else is accessory if we don't want to commit the no true scotsman.
Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you