I don't believe theists and reject their claims of theism.

[Neo-Scholastic]

On what grounds is anyone able to assert claim of a God and then stamp it as rational?

I for one am of the opinion that a rational understanding of the physical universe depends on presupposing forces and principles that operate parallel to, in tandem with, and above those of the physical universe. That was certainly one of the implications of Godel, Escher, Bach. My point is that reason itself depends on something over and above what can be known purely by empirical observations.