but John Loftus is getting dangerously close to flirting with presuppositionalism!.

That’s right, with comments like: “”Plus, when it comes to ‘initial plausibility,’ we’re talking about metaphysical issues with background and control beliefs that go with them, on both sides” and “Convincing someone to believe something different and to see the unreasonableness of their position contains an irreducible personal element to it, not reduceable to logic itself” and “As I said, some informal fallacies are merely anomalies to another world-view perspective, and that’s all”

Yes, this background stuff, this “irreducible personal element”–those are our presuppositions, the unproven (indeed, in properly basic presuppositions, unprovable) axioms that someone must assume in order to begin thinking in the first place.