That being said, I will return to your nine points, because I do not have time to examine them in depth now, but I certainly think it is possible to say "That's just the way it is" or "we don't really know" and not pass into the realm of religion (unless your definition of religion is so broad as to, by definition, include atheism. In such a case all you are doing is proving what you set out to define, by referencing your definition.)
In other words, it appears to me that you work from the assumption that absent disproof of these points, no non-religious belief system can exist. You have thus put the rabbit in the hat, by making the default value "religion." In doing so, you make non-religious uncertainty, insufficient data, or even an arbitrary natural state to be evidence of religion or religious belief.
I would first state that I think your main thesis is flawed, because one need not be strictly rational to be an atheist. Thus, requiring "a scientific or mathematically plausible explanation" conflates the two.
Yours is an interesting post, and I will return to it when I have time.
Indeed, the question of "what is a 'religion'?" is pivotal to my challenges. That is why I included the link, to explain why atheism is considered a religion, especially wrt politics and 1st amendment rights.
If a person is atheist or even simply agnostic without considering and/or answering any of the challenges, that is fine. But such a reaction is a belief and thus "materialism" and in particular "scientific materialism" from such a one is on par with similarly biased theological arguments about origins and life. IOW, in that case the notion that a person is atheist by reason cannot apply - scientific objectivity is out the window.
Also, "doubt" does not equal atheism. Doubting Thomas was an Apostle, too.