If you give reasons either way---for atheism or belief that God exists---either those reasons or whatever principles justify those reasons, are already the God-level, root access mind-governing system indicating what you ought to believe, a higher-level set of claims that work together and “tell you” the ground rules and whether or not conclusions are true.
That statement-evaluating system functions as an invisible cognitive friend, and is indistinguishable from a real one that might come along.
And this is empirically verifiable. Merely chronicle for yourself how people justify their belief or non-belief or disbelief in the existence of God.
In other words, to think rationally at all, is to already function according to an ultimate ideality or even god of thought---depending on how you construe personhood. One cannot really argue against this ideal system without thereby using that same system as the ideal for guiding that case-building logical process itself.
It doesn't have to be identical in details in all minds for this point to be true. It just has to be true about some necessary core of rules, identities, and other relations. Necessarily true of necessary statements.
Denial here tries to do what it says this kind of system theory cannot do.
