There's no argument with the fact that people since the beginning and for whatever reason have committed atrocities sometimes too horrific to imagine. There is an argument, however, when any historical event(s) is referenced but judged outside its proper context. This is what the president did. The Crusades (officially, more or less, between 1098 and 1291) represented contests for territory more than for religious reasons in that the Muslim thrust, perhaps beginning with the conquest by Muslims of Jerusalem in 638, had to do with subjecting whole populations and their territories. This would be akin to the Baptists attempting to take over Catholic New Orleans...a land-grab.
Muhammad (530-632) was a caravan-raider and also participated in tribal warfare. In 610, he declared receiving revelations from Allah through the angel Gabriel (apparently co-opted from Holy Scripture), began preaching to his own tribe and claimed his position to be that of prophet. His “brethren” in Mecca would have none of it and he was forced to make his headquarters in Medina in 622, from where he and his followers remained solvent by raiding caravans, with horrible violence part of the action, not to mention vindictiveness against the “brethren.” Not long after, Jerusalem fell, thus the contention established between the followers of God of the Bible and the followers of Muhammad.
The Islamic movement headed west throughout North Africa and even into Spain (Muslims called Moors), an actual invasion of Europe, in 711. The Moors ruled Spain until they were defeated in 1492 at Granada by the Católicos (Catholics). In the meantime, Muslim forces contested with Christian (actually mostly Catholic) forces back and forth as Muslims (remember the great Saladin) tried to take over Europe, with the Crusades organized to push back. The battles didn't stop in 1291 but continued for centuries into the 1600s...Ukraine, Vienna, Poland, for instance. The Muslim effort was always to establish the worldwide Caliphate, the announced goal of ISIS today.
The battles were actually wars no different from wars today, for territory. It happened that they pitted Muslims against Christians, each faction claiming divine ordination from Allah (actually Muhammad) and God of the Bible, respectively. So, Crusaders fought in the name of Christ, something for which everyone in Europe and the U.S. should be proud and grateful. Imagine Sharia Law in all statehouses, courthouses and in Washington, especially as applied to women.
The president's allusion to slavery and Jim Crow as being justified in the name of Christ comprised a cheap shot. There may have been some zealots back in the day who approved and/or preached that contemptible position but there was never any movement—at least to my knowledge—which had as its focus God of the Bible ordaining slavery. The entire world economy almost from the beginning of the human race was built upon slavery, the strongest subjecting the weakest. Scripture-writers dealt with it as a fact of life ordained by morally challenged people and even included rules dedicated to the treatment of slaves, but the practice was conducted in the name of homo sapiens.
The president made a feeble attempt to tiptoe around what everyone in the room knew to be a curse on the world—militant Muslims conducting jihad, the actual proponents of slavery as exercised against the infidel. It's called Dhimmitude. Officials of Islam, as must all Muslims, admit that according to the Koran the infidel is to be killed, pay a tax or become a slave. This is sort of understandable because Obama's entire childhood was Muslim-oriented. Using a prayer breakfast to further divide people into camps, however, by trying to get them to “understand” what is beyond comprehension, to wit, more than a billion Muslims worldwide failing to neutralize murderers claiming divine impetus for genocide—often torturous beyond belief—was disingenuous, dishonest, totally out of place.
Of course, it could be that the president is ignorant of the history. That's even worse.
And so it goes.