Medieval Christian anti-Islam polemic relied on scripture, not rational argument.

Evidence

While effusively expressing his admiration and respect for philosophy and ratio, Peter is certainly not adept in the scientific-rational forms of argumentation common in the Risâlat al-Kindî, Petrus Alfonsi’s Dialogi, and other such works. He is much more at home when he can marshal his formidable knowledge of scripture to refute Saracen errors. — John V. Tolan, Saracens, 868