What the atheist is fundamentally saying is that he has infinite knowledge of this universe to affirm that there exist no being with infinite knowledge. What the atheist is fundamentally saying is that he has infinite knowledge of this universe to affirm that there exist no being with infinite knowledge
The problem is you haven't defined the "God" that atheists reject.
Christians make a lot of specific claims about god. It is possible to show that these claims cannot be reconciled with each other or with reality. Therefore we can say with certainty that the god of Jesus does not exist.
If you retreat into a very vague form of deism - a common trick of christian apologists - then of course your very modest claims can never be refuted.
To illustrate - If I said unicorns exist, an a-unicornist could never prove me wrong without perfect knowledge of all the beings - visible and invisible - in the universe. If however I say that a large pink, visible, and noisy unicorn lives in my bathroom then the a-unicornist could prove their case beyond all reasonable doubt.