4/10: Metaphysics Γ 7-8 (discussion opener)

In chapters 7 & 8, Aristotle defends the Principle of Non-Contradiction as the strongest and most fundamental principle of all. He says it can't be demonstrated because demonstration already presupposes it, but also insists that it's not possible to meaningfully deny it. Someone who tries to reject this principle can still be disproved by being shown to contradict themselves in speech & the way they live.

This seems to me like a strong claim. Aristotle appears to be saying that denying the PNC isn't just wrong, but unintelligible. If all we can do is show that someone contradicts themselves when they deny it isn't that just assuming the principle in order to defend it? If that is the case is it actually being defended, or just asserted in a different form?

Also the move to say that even people who say they reject it still live as though it's true seems to shift the ground a bit. Is that a fair way to settle a metaphysical disagreement? Should metaphysics rely on how people act rather than on what they can consistently argue?