Interesting, from a reader:

Dear Mr. Goldberg,
One winkle always worth mentioning is that the majority of the
inhabitants of the Levant were almost certainly Eastern Orthodox,
Monophysite, etc. at the time of the First Crusade–the cities *may*
have largely converted to Islam by the time of the First Crusade, but
the peasantry probably remained largely Christian of one sort or
another. Therefore, both Catholics and Muslims were fighting for
domination over a people alien to both. (And to the extent the locals
were Monophysite, alien to the Byzantines as well!) There is a
long-standing thesis that Muslims were somewhat more tolerant to Eastern
Orthodox and Monophysites than were Catholics, and that the final
victory of the Muslims had something to do with the local Christian
preference for Muslim over Catholic rulers–possibly so, though I
wouldn’t go all gooey about medieval Muslim tolerance. There’s an
interesting-sounding book I haven’t yet read, Ronnie Ellenblum,
/Frankish Rural Settlement in the Latin Kingdom of Jerusalem/, which I
believe indicates there was already a substantial Catholic settler
population (400K?) by the time of the Muslim reconquest–settled for up
to a century, and by then somewhat amalgamated with the local Christian
population. This further complicates the story, and whatever morals one
wishes to draw.