Sea Breeze: Is there some rule of logic that states that it is "wrong" to examine where the brain comes from to determine if it is a reliable, trustworty and accurate guide ?
There isn't. But you are asking me to defend something I did not claim. My explanations are, as far as I can see, complete. They do not require a god, and they do not require a big bang. Either of those is an unnecessary addition to the explanation, and would require justification on their own.
It is as if you had asked me why a rubber ball bounces, and I explained that one of the properties of rubber is elasticity, and this causes the ball to bounce. That explanation is complete, and requires no further additions. If someone wants to prove that rubber was a divine creation, they are welcome to explain themselves. If the explanation is a demand that I show how the big bang created rubber, I would point out that my explanation does not require this. Rubber balls bounce because rubber is bouncy. Humans use logic because our brains are capable of rational thought via deduction and inference. Anything beyond that must be proven by the person making the additional claim.
As for the atheist worldview: I have mentioned before my issues with big bang cosmology, which is that the explanations do not make intuitive sense to me. I accept that scientists have a model, and that they have explanations, but those are complex and not easy to grasp. I do not claim that they are wrong; I accept that I may simply be ignorant or lack sufficient education. This is fine. The world works as it does, and while I am open to the possibility that gods exist, I have not yet found one that makes sense. Indeed, the gods that make the most sense to me are ones that we will never get to know, or even know of.
If the atheist worldview demands that I accept things that I cannot accept, then I don't share the atheist worldview. And I can't defend something I don't believe, not very effectively, anyway.