If he thought that materialists became materialists by reasoning correctly, he would either have been a materialist, or would have taken one of a particularly narrow set of positions (such as "materialism is based on correct reasoning, and how something can be false and correctly reasoned at the same time is one of God's mysteries" or "materialists are only materialists because they start with different premises from me, but correctly reason from those premises") which as far as I know he didn't. (Or else taken no opinion on materialism, which he wasn't going to do.)