Clearly lot of the people Saletan is quoting are being apologists, sometimes with a side of bigotry, rather than historians. But the reality is that many of their apologias are still closer to the historical reality than his snideness about the alleged “awkward gap” between Islamic aggression and Christian crusading. Like all complicated historical events, the Crusades were hardly monocausal, and historians will be arguing about the whys and wherefores in the same way that they’ll always argue about the causes of the last century’s global conflicts. But the first Crusade was not summoned, as Saletan implies, in a world where the Islamic empires and Christian Europe had been enjoying a comfortable four-hundred year peace after the original fall of Jerusalem to Muslim armies. Instead the actual context included 1) the gradual rolling back of prior Muslim conquests in Spain and Southern Italy (Saracen raiders had threatened Rome in the 10th century, and the Emirate of Sicily only fell to the Normans five years before Pope Urban II called the First Crusade), 2) the disastrous Byzantine defeat at Manzikert in 1071, at the hands of the Seljuk Turks, which ended with the emperor in chains and prompted Constantinople to call for military assistance from the West, and 3) the Seljuk occupation of Palestine (displacing the Fatimid Caliphate), which visited persecution and pillage on the Holy Land’s remaining Christians and made pilgrimage much more difficult than it had been under some (though not all) of the Fatimid rulers.
The context also included many other factors internal to Western Christendom, which is why historians have wrangled endlessly over the motivations of Urban and others, and over how much explanatory weight to give to geopolitical issues related to Islam versus other goals (increasing papal power, channeling intra-Christian violence elsewhere, forcing a reunion with Orthodoxy, etc.). But the broad story of the era and the movement can’t be explained without a recognition that the context of the crusades, from the 11th century beginning to the echoes at Lepanto and Vienna centuries later, always included 1) ongoing conflict between Islamic and Christian forces in territory that had been Christian before an earlier wave of Muslim conquest and 2) the emergence of new Islamic powers, first Seljuk and then Ottoman, whose advances threatened first Byzantium and then, after its fall, the Balkans, the Christian Mediterranean and eventually Central Europe. One can argue back and forth over whether this or that crusade met “just war” criteria, but none of them sprang de novo from a world of stable borders and religious peace, and all of them were part of a longer story of attack and counterattack in which both sides were playing for potentially-existential stakes.
Which makes a comparison between the Crusades as a historical phenomenon and various specific institutions — the sort of comparison in which “Crusaders” get casually likened to “slave owners”, for instance — seem, well, not even wrong: It’s just a category error, like putting “Franco-British conflict from the 14th through the 19th century” on the same list of great historical wrongs as South African apartheid, and then when challenged invoking Henry V at Rouen and the Vendee to “prove” your point. And it’s a category error that Christians, and especially Catholics and other Christians who aren’t pacifists and don’t think the true faith died with Constantine, can’t reasonably just acquiesce to and accept, any more than a patriotic Frenchman should accept some blanket historical condemnation of “French aggression” that casts Charles Martel, Joan of Arc and the Marquis de Montcalm alike as great historical villains. The Crusades as an epoch-spanning phenomenon aren’t in and of themselves a great stain on Christian history: They’re a phenomenon in Christian history that includes many stains and sins and great crimes, but also involves many admirable figures and heroic moments, many great tragedies, and many individuals and incidents that simply resist any kind of manichaean reading. Contemporary Christians should reject and disavow the great crimes that some Crusaders committed as they should reject and disavow the un-Christian hatreds that motivated them. But we are under no obligation to reject and disavow the entire multi-century struggle with an armed and equally-militant foe as merely the manifestation of some irrational religious “phobia,” let alone accede to analogies that cast an entire civilization’s worth of kings and theologians and soldiers as the moral equivalent of Osama Bin Laden.