Rebecca Writes gives some thoughts on the KJV-only position. Much of what she says isn't directed toward the more moderate position like Mac's (which I've discussed here), but some of what she says might apply to his position. On the textual issue, which is one place Mac agrees with the KJV-only position, she expresses one thing that I didn't think I made clear enough:
They have already made up their minds about the way they think God ought to have preserved his word, and it would be difficult for them to keep trusting in a God who may have done things differently than the way they think would be the best way.
I think that's exactly what's going on in many cases. There's an a priori commitment to a principle about what counts as God preserving his word, and that principle by definition rules out the richer textual tradition that I've argued will help us to capture better what the original text said. Yet nowhere in scripture is such a principle stated.