So what, some of them are extremists and terrorists!
Think about it. In midevil times Pope Urban (in my opinion one of the WORST MEN TO EVER WALK THE FACE OF THIS EARTH) ordered a violent attack on Jeursalem to take it from the Muslims.
Actually, Christianity and Islam had coexisted for quite some time... when the Center of the Islamic World had been Damascus. But there was a War within Islam and the more Radical and Hardcore Bhagdad took over things. A squeeze was put on both relations with the Christian World and on the more liberal Muslims in the Holy Land, North Africa, and Spain.
Things only got worse as the Mongols from the Far East took more and more control over the Islamic Centers.
Truth be told, many Provincial Islamic Powers had appealed to the Catholic Pope for assistance against the both the Mongols and the interferences of the Imans in Bhagdad.
So just to insist that the Crusades was simply about attacking Islam... it pretends that Islam was somehow united and monolithic. It wasn't. Many of the Muslims were rooting and cheering for the Frankish Knights.
Oh, about the Sac of Jerusalem. Well, all that is very unfortunate. But the Franks were indeed seriously outnumbered in the region. They were able to gain local support by promising various Business Concessions to surrounding business interests. These would replace business interests that had currently been active in Jerusalem. If allowed to survive, they probably would have complained about the arrangments. War is nasty, isn't it? But, on the other hand, the people of Jerusalem and indeed the entire Near East had screwed up by not strongly enough supporting the Moderate Powers in Damascus, and then in allowing the Mongols such as easy cake walk when they invaded and took every Throne in the Region.
So, the Christian Forces were only fighting in a Region that had already been entirely invaded and defeated -- by the Mongols. And if they had not stopped the Mongols at Jerusalem, then Europe would have been next. Indeed, when the Crusades finally turned sour and the Christians were put on the run, the Turks, this time, were able to march as far as Vienna before they were finally stopped, but it could have been Paris or even London.
Oh, and by the way, people forget that Islam is a relatively recent Religion. It would have been only a regional religion in the middle of the Saudi Desert except that they launched a huge military invasion against the rest of the World. Their big mistake was to convert the Mongol Huns and Turks who fully assimulated the Islamic Doctrines of Sword and Violence and turned it against the Missionaries who had converted them. That is the problem with teaching people religiously that Violence is the solution for every tiny little problem... that your students will eventually see you as one of those Problems that need solving.