Where do axioms come from?

While reading @dwinblood's post about the fallacy communism this little fragment got my attention:

I am not religious, so when I say "this is evil" it has nothing to do with religion. It has to do with simply knowing that killing someone for thinking different things than you do is wrong.

How is it that there are things that "we simply know"?
Where does this knowledge come from?

To be clear, I am not trying to tease @dwinblood, that's an honest question. That's something that intrigues me a lot lately. Many of us declare not being religious, yet there seem to be some sort of set of axioms which are true to us without any rational or scientific proof.

Where do those axioms come from? They cannot be verified by anything we have at our disposal. So do they come from outside of our reality? If so, why not call them God?

@dwinblood says that "it has nothing to do with religion", as if religion was something unreliable. But maybe his statement actually is the very essence of religion? As it deals with things that seem to be way more primordial than the reality we have access to.

What if we defined God not naively, as some angry old man creating stuff, but instead as the domain where our axioms come from?

On the other hand, if we deny the existence of this external domain, then we imply that the reality we live in just created itself by some sort of bootstrapping mechanism.

I used to think what way until I realized that nobody can give me any example of anything that us capable of this trick. Not even in such abstract areas as mathematics - every mathematical theory needs to have some external axioms which cannot be derived from within the theory.

So maybe blockchains? They are known for their bootstrapping & self-validating capabilities.
No, not even them - every blockchain has its origin outside itself.

So why do we believe in the bootstrapping theory, if we have not seen a single instance of it?

For me it's just as irrational as believing in God. Or even more irrational because by rejecting the concept of an external reality you believe in something that does not exist, not even mathematically: a self-contained entity.

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