Medieval Christian writers saw captive concubinage as Islam’s gravest offense

Evidence

Christians were naturally particularly sensitive to the acquisition of slaves in warfare, and were very concerned about the fate of their women when they were taken prisoner. Islamic law allowed these to be made concubines. Ricoldo was here a little confused, although his statements show some understanding; he noted that men had sexual rights over both their wives and prisoners of war (concubitum tam cum uxoribus quam cum illis quas in bello ceperunt); but he also complained that it was not enough that the Qur’an should forbid women to be forced, without forbidding women freely to consent. With regard to the forcing of women, his statements conflict. — Norman Daniel, Islam and the West, 780