Darwin's "horrid" doubt, in context

Proponents of Alvin Plantinga's evolutionary argument against Naturalism (EAAN) often quote Charles Darwin's 22 April 1881 letter to William Graham to imply Darwin worried that his theory of evolution committed its adherents to some sort of global skepticism. This niggling epistemic worry has, therefore, been dubbed 'Darwin's Doubt'. But this gets Darwin wrong. After combing through Darwin's correspondence and autobiographical writings, the author maintains that Darwin only worried that evolution might cause us to doubt (a) particularly abstruse metaphysical and theological beliefs, and (b) beliefs arrived at by 'intuition' rather than evidence-based reasoning. He did not worry that unguided evolution should lead us to doubt all of our beliefs in the way Plantinga and others have implied that it does.