would you say The Crusades were just some whack jobs and not representative of Christianity? it's not a trap, i'm genuinely curious.
Which one? The first crusade was a power grab by Urban II and the Church by seeing the writing on the wall, the Muslim world was being pushed out of mainland Europe and the church, being the "wests" most dominant central power, saw this and attacked the Caliphate to secure it's own position. Lords went along with it out of both piety and self interest, in order for them to unify their people under a divine mandate. While religion was the justification of the conflict, it wasn't the driving force behind it's major actors.
The second was simply a counter offensive by the European powers to drive back the Turks from Edessa. It failed, but powers on the mainland used it to consolidate Ibera (Portugal began it's rise as a European power from it).
The third was another defensive against Saladin.
The fourth, well, that was just an excuse to conquer Byzantium.
Christianity formed the spine they used to justify the wars, but it was never actually about "retaking the holy land", in fact more gains were made in the crusades in Europe proper than ever were by crusader kingdoms.
The situations are different because ISIS/ISIL is a purely modern middle eastern creation, a radicalized Wahhabi army comprised of various tribes that banded together through extremism but, in actuality, the fighting is mostly sectarian, as it's all against other tribes in the regions even if they are adherents.
Christianity at the time was either the eastern Orthodoxy (which two of the crusades were de facto waged against) or Roman Catholicism, the Catholic west banded together as a means of convenience, less so than any sort of grand piety. As he had been for hundreds of years, the Pope was more used as a symbol of legitimacy of rule, less so as a purely divine religious analogue or figure. The Crusades were never
really a holy war except to the poor farmers and levies that were raised by various lords. But blaming them or saying that their zeal is vlaidation that it was a religious conflict is like saying the brainwashed kids from Madrassa know what they are doing.
Most of the time they had no idea where they were even going.