It's a foolish argument.
A good tree is intrinsically good. A Child of God will intrinsically believe. They may have a season where they think they lost their sonship, but they still know WHO the Father is. They may think THEY messed up so much that the Father has disowned them, but we KNOW the Father is drawing them back, searching for them UNTIL He finds them, and then He will hug them and kiss them. Why? BECAUSE THEY ARE HIS KIDS!
They don't suddenly think shiva, krista, allah, zeus, etc.... are the Father.
So to reiterate, a born again Child of God may for a time have doubts who THEY are, but they never disbelieve who God is!