IOW, the Turks, when they took Constantinople, behaved pretty much as other armies of the time did when they captured a city after an arduous siege. Much as the Crusaders did when they captured Jerusalem, by their own account.
The author is correct that ISIS behaves pretty much as Islam did in its heyday. The difference being that was pretty much how all armies behaved back then. Read about the Sack of Rome or Magdeburg, for instance.
I would also note that it is possible to take pride in the deeds of one’s ancestors without necessarily approving of their methods. Much as I am proud of the Founders without approving of the fact that many of them were slavemasters.
How dare you site actually history, and place things in their proper historical context.