The problem here is that this defence of the authority of human reason is ultimately circular and parasitical. It assumes and depends upon its conclusion. This philosophical defence of the validity of reason by reason is thus intrinsically self-referential. It cannot be sustained.
The rational defence of reason itself may amount to a demonstration of its internal consistency and coherence – but not of its truth. There is no reason why a flawed rationality will show up its own flaws. We are using a tool to judge its own reliability. We have convened a court, in which the accused and the judge are one and the same.
Reason needs to be calibrated by something external….
Actually, I think Descartes’ meditation on the existence of God is kind of helpful. And the way he delineates the “idea of God’ hardly constitutes an invention on his part. Admittedly it is impersonal. Still, I believe there is limited value in these sweeping historical generalizations.