There are a lot of questions to unpack here, so I'll stick to the most fundamental one.

Atheists would be happy to believe in any god that would evidence itself. In the meantime, they do not believe the un-evidenced. That doesn't preclude them from seeing a sound reason to believe in god at some future time when he might deign to substantiate his own existence.

I don't think I'm a "non-existence certainty" atheist, nor, when pressed, are most of us. For two reasons. First ... nothing is 100% objectively certain. I haven't been everywhere and everywhen, so sure, there might be a deity hiding under a rock somewhere that I haven't overturned. Although out of respect for hiding deities, I prefer to grant them their privacy. After all, there's no way to distinguish a hiding, absent, indifferent or non-existent god. They all behave EXACTLY the same.

And #2 ... invisible beings and realms are, inherently, non-falsifiable and therefore non-[dis]provable. As such, no supportable knowledge claim can be made for OR against their existence. Still ... absent evidence, or even really the POSSIBILITY of evidence (given non-falsifiability), I do not believe and I legitimately consider the probability of the existence of some generic god, much less some specific god, to be quite tiny indeed.

And #3 while I'm at it -- gods don't add any explanatory or predictive power to an understanding of reality. They are not necessary entities. In fact, they muddy the waters rather than clear them. Thus they violate Occam's Razor.

I'm more of an agnostic in that I don't know. I do believe there are things beyond our knowledge, that there is a higher power or a universal oneness, but I don't attribute to anything concrete. That being said, I think there are fundamentalists of every sect, including atheists -- anyone who believes that their way is the only way and everything else is wrong.

It's just a belief to me but if there is one he is one nasty horrible fucker.

Most comments that I’ve seen on this site all say that the reason these individuals don’t accept that a god exists is lack of evidence. There is no difference between their lack of belief in god than there is in fairies, unicorns, UFOs, or any god other than the one you happen to envision. If you wish to believe in something without any definition of what that something is then that something can be logically dismissed. That belief becomes nothing but faith which is believing without any evidence.

It's likely the universe couldn't have come by chance or maybe it came by chance. But I feel like there was a cause and something or some higher civilization caused it to be, "how did the first cause come about?" I see this question as an intellectual question. Obviously, the gods described in the various religions couldn't have been the cause; they couldn't even describe the universe in a factual way. If the cause of this universe came from a higher civilization, maybe the universe is a kind of hugh machine in their own plane, we may never know. Maybe they caused the universe but humans and other living things came by accident through evolution, maybe that's why they don't care about what we are doing because they do not have knowledge of our existence. Or maybe they care but the task is just too overwhelming for them. Or maybe they are just watching us in silence as a form of their own entertainment and reached a consensus never to interfere. Or maybe the higher civilization also came by accident in their plane and decided to be the cause of our plane. Whatever the case may be, it seems that the answer to this question is beyond our grasp. Maybe we could figure it out in future. So much speculations . I'm completely agnostic about it.

OK, I do not believe in a god, that may change if I was presented with suitable evidence.
You cannot prove that anything does NOT exist, so I cannot prove a god does not.
But, there is no evidence that proves that any god ever mentioned exists and the bible is proof of the non existence of the God of the Bible as the Bible is just a whole bunch of contradictions. The universe has existed for billions of years before humans, so who could record what happened?

For me, I'm all but certain that there are no gods based upon logic and the overwhelming lack of evidence that any gods exist. Sure, the possibility that an all-knowing, all-powerful entity could exist, but if so, it has removed itself from having any meaningful influence on our existence as far as I can determine. If there is some entity that has chosen to have nothing to do with our world, then its irrelevant that this entity exists much the same way that its irrelevant that parallel realities might exist but they will not have any impact on this reality.

But, 1000 years ago, there was evidence (though maybe not recognized as such) that electrons and protons existed. And atomic theory was actually first theorized more than 2400 years ago.

My thoughts are faith based. To be religious, you have to have faith. Faith that there is a god, faith that you will go to a better place when you die, or faith that if you are a bad person, you will go to hell. I have no faith in all of that, so..... guess what! I don't believe in god. I believe in myself. That works for me and proudly, most of the people on this site.

I think it depends on one's definition of "God". For our purpose this God is anthropocentric. It is fear of mortality that drives the religious. Their God is full of emotions which we know are stimulated through chemical reactions. We may not fully understand the reason for the emergence of material but it is certain it does not happen through supernatural means.

This is the old "You can't prove it's not true," argument. If that's the standard by which we measure certainty, we're in a lot of trouble because you can't prove something doesn't exist.

I feel the same way. I find it amusing that people think they can lock down what a god would be like, and logically disprove its existence on that basis. How could you possibly know any of that stuff? Why would a god have to conform to your notions of logic?

Why would a god have to love you--or care about you at all--or even know you exist?

Why would a god have to be good? Or evil?

Why would a god have to "know" anything? Or care about, or want anything?

Why would a god have to do anything or be anything that makes sense to us?

Before anyone says, "Because it wouldn't be a 'god', otherwise...": how could you possibly know your definition of what a god is or should be would be accurate?

I do not believe in some entity as God! But, it was Einstein who proved that all life is energy, but vibrates at different speeds...which takes different forms. So for me, God...is a force! We harness that force into all kinds of things! Even evil! I don't believe there is nothing! But at the same time...I do not believe in some God!

An unanswerable question not worth pondering.

There has never been any evidence, facts or data to indicate that any god(s), deities, "higher power", supernatural exists and until some verifiable evidence, facts or data is produced, then said god(s), deities, "higher power", supernatural does not exist. In My Humble Opinion.
ETA: "What can be asserted without evidence can be dismissed without evidence". Hitchen's Razor
"Extraordinary claims require extraordinary evidence" Carl Sagan