Theism/religion is a learned category of belief/culture/behavior.
No, it's not. Theism is a logically derived existential proposition. Religion is the life practice based on a specific interpretation of that proposition. Now, please explain logically why you think this is wrong.
Many folks in the USA aren't religious and don't really have an active position on any of the many religious options.
How one responds to any given religious depiction of God is irrelevant to the theist proposition that God/gods exist.
But if asked they tend to answer that they believe in a God.
What they believe is not relevant to anyone but them. And what they believe does not define the terms; theism, or atheism, or religion, or the color purple.
These passive "believers" have a position, but it is one that came from social conformity and not an active and engaged belief.
Their belief is irrelevant. The intensity of their belief is irrelevant. What is relevant is what they assert to be a valid concept of reality relative to the theist proposition, and how they logically support this assertion.
Such folks who don't really think about religion or any gods aren't atheists, they are essentially in intellectual limbo.
It doesn't matter to anyone what they do or don't think about. What matters is what they assert to be a valid concept of reality relative to the theist proposition, and how they logically support this assertion.
I don't consider then as having a position.
They either assert their position and validate it logically, or they don't.
Atheism tends to be a category of people who have thought about religious claims (typically supernatural) and have rejected them intellectually.
What they thought about religion is not relevant. No one cares what anyone thinks about religion. The question at hand is, is the theist proposition that God/gods exist valid? The question at hand is NOT which God or gods exist, or how, or to what purpose. Because those question are all predicated on the having already accepted the the theist proposition as valid.
These are active positions.
But they are not philosophical positions. They are responses to various religious depictions of God/gods intended for people that have already determined that the theist proposition is valid.
Even agnostics (which I assert is everyone since there is no way to know anything factually about the supernatural claims made by religion) are a position and one that has engaged with whether they have an intellectual reason to believe any of the religious claims they have encountered.
Agnosticism, specifically, is a position regarding the possibility of our being able to know an extant God. Like religion, it is predicated on having already accepted the theist proposition that God/gods exist. Not knowing IF God/gods exist is, as you point out, a fact of reality for all of us. And is therefor not at issue.
I would agree that non-belief is not necessarily non-theism (atheism) since theism itself is a category of complex and abstract ideas.
Theism itself is just the proposition. How we respond to that proposition varies from absolute dogged religiosity to equally dogged indifference.
But negating someone else's response does not negate the original proposition. And this is something that many atheists around here are working very hard NOT to recognize.
Yet logic isn't used to conclude that religious concepts are true, it's faith. Believers actually brag about it.
Again, this has nothing to do with the actual theist proposition. It's just another of the many ways people will choose to respond to it.