I think you may be conflating things a bit. Atheism is simply a lack of belief in gods, it doesn’t automatically come with a particular worldview. Worldviews are much more broad, as the name would imply. They encompass a set of values and assumptions about life. Atheism doesn’t prescribe how someone views politics, morality, or society. Those are shaped by other philosophies like humanism or existentialism.
I agree that no one is immune to the dysfunctions of collective action, and atheists can certainly fall prey to the same human errors and biases that affect any group. However, attributing those flaws to atheism itself misses the point. The fact that individuals with different beliefs, whether religious or non-religious, have varying behaviors doesn’t stem from atheism as a ‘worldview’—it’s part of the complex nature of human society.
Criticism of specific worldviews is valid, but atheism as a simple lack of belief in gods doesn’t operate on the same level as belief systems that come with doctrines and tenets.
Perhaps (as i mentioned before) or can be called merely a fundamental aspect of a world view, as in “an atheistic world view”.
I suppose I so tend to say “an atheistic world view” or “a theistic world view” when talking about the matter. That indicates more that it’s a fundamental characteristic of the world view, when compared to other world views, and not necessarily the world view itself.
By nature of the subject (gods being, in general, vast entities fundamental to the structure of the world), atheism is at least a fundamental aspect of an atheistic world view. That is, like magical unicorns, one couldn’t simply drop a god into an atheistic world view and have the people who hold that world view accept it without some serious issues.
I think being non-unicornian is also a fundamental facet of most atheistic world views.
Of course, ”non-unicornian" is a bit tongue-in-cheek. A somewhat better term might be “non-fantastical world views,” but whatever.
