Not really sure what your point is. Newton believing in alchemy didn't make him any less smart, and for what it's worth, alchemists didn't so much 'believe' in alchemy as they believed it was a methodology that could offer useful knowledge, much as scientists today believe that the scientific method can offer useful knowledge. And alchemy did in fact offer a number of important breakthroughs in our knowledge of the natural world. Was it as flexible and powerful as our current scientific method? No, but looking down on people for making use of the best available techniques for advancing physical knowledge is no better than looking down on people for making use of the best available techniques for advancing spiritual knowledge. Which is, in fact, Guillen's point.

Note that my critique of Guillen isn't that he's trying to prove that intelligent people can believe in God. It's that his methods of doing so are simple and obvious. I found the book boring, not wrong.