Tactics or morality?

From Carnage and Culture by Victor Davis Hanson. Page 155.

There were numerous early Islamic historians, many of whom were candid and remarkably critical, but few saw history as really existing before the era of the Prophet (thus the maxim “Islam cancels all that was before it”). And the parameters of inquiry were limited by the Koran, whose literary and historical primacy tolerated no competition from mere mortals. Contrary to classical historiography — there seems to be little evidence of any early Arabic translation of the major Greek historians — lapses in morality, not tactical blunders or structural flaws, were cited as reasons for Islamic defeats. After Poitiers, Arab chroniclers, as would be true of Ottoman observers in the aftermath of Lepanto, attributed the Muslim slaughter to their own wickedness and impiety that had brought on the wrath of Allah.