There is no fact that can demonstrate that G-d does not exist.
Nobody claimed otherwise.
You are operating from a false dichotomy.
I don't require reasons to NOT believe something.
I require reasons to positively believe something. And when I then find out that my reasons to believe something are actually lacking, then I stop believing it.
Also, it's not merely a question of god existing or not. A lot more comes into play.
Take Thor for an easy example that we likely both agree on.
Suppose you hold a belief in Thor and thus also the lore that comes with it. Like thunder and lightning being the result of him smashing his hammer.
If you then find out that thunder and lightning actually has rational physical explanations and thus aren't the result
at all of any gods smashing any hammers, then that will likely shake your entire belief system.
This might very well trigger you into abandoning your belief in Thor.
Even though no facts were learned that showed Thor to not existing.... Instead, you found out that things that are attributed to Thor, actually don't have anything to do with Thor at all.
So what you previously considered to be evidence FOR Thor, turns out to not be such at all.
Suddenly you are left with a claim of Thor that isn't in evidence. You no longer have any reason to believe it. So you stop believing it.
See?
..so while I agree that we can learn new things and form opinions, it is not the only factor as you are claiming.
I say it mostly is. At no point do "arbitrary choices" come into play when it comes to deciding what you will and will not believe. Belief is not a decision or choice. It's a compulsory conclusion based on reason and evidence. Regardless of that reason and evidence being accurate or not. At the time, you obviously think it's rational and accurate. When you find out that it isn't - that's when you'll likely alter your compulsory conclusions.
Reason and evidence is how you get convinced of things.
So it's also through reason and evidence that you'll change your mind.
Not through arbitrary choice.
We most certainly can choose to be open-minded .. or not.
"open-minded" - I don't think you understand what it means.
Being open-minded doesn't mean that you'll lower your standard of evidence or whatever.
It doesn't mean that you'll "more easily" believe something.
Instead, it just means that you are open to
new information. That you are open to the idea that your beliefs might not be correct. That your reasons for belief might not be rational or accurate.
A closed minded person is someone who will refuse to question his beliefs, refuse to accept the possibility that he may be incorrect.