Chalmers is a naturalist who explicitly rejects theistic explanations of consciousness. Isn’t using him for a theistic argument borrowing his premise and ignoring his conclusion?

Chalmers is not arguing for God, and he is used here for the premise only. That is legitimate as long as it is clear that his own solution, consciousness as a fundamental property within a naturalistic framework, is a rival to the theistic one, not a step toward it. The fork is this: if the hard problem is real, reductive physicalism is in trouble, and both a mind-first universe and Chalmers’s naturalistic dualism are ways of taking that seriously. Which fits better is the comparison the next exhibit makes.