I would argue that any religious group that names itself in a way that suggests its primary attribute is a rejection of atheism could be effectively paired against atheists, while any religion that names itself in terms of what it believes (which includes all of Christianity, Judaism, and most other religions) would be comparable to humanists, not atheists.
Humanists and atheists are the same group. There is no significant difference between them, except that humanism is about what they do believe, whereas atheism is about their rejection of God and religion.
So I think it’s perfectly fair to treat “atheism” as different than religion. When people who embrace the Enlightenment’s core beliefs are describing themselves as atheists, they are doing it as culture warriors arrayed against the enemy religion. When these same people are pursuing positive goals, rather than negative ones, they themselves tend to prefer the term humanist.’


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