Christianity makes an easy target for a plethora of reasons.
I won’t pile on the insults. Doing so only makes me look upon myself as weak.
I like my evangelist to be silent in their speech but loud in their actions. Let your life be your message.
Ok, now on to the Crusades. There is no one answer for this complex chapter. They were a military response to the militant spread of Islam. They were a political movement in that the Roman Emperor (Sorry folks the Byzantines saw themselves as Romanoi) agreed to acknowledge the Metropolitan of Rome, or Bishop of Rome, as having primacy over the all other churches.
Then there is the social piece. Primogeniture left a lot of surplus men throughout Europe. Excess male population can lead to instability, so send them off to war.
Then there is the great motivator of so many wars, $$$$. Muslims cut off trade, Muslims controlled some of Christianity’s greatest pilgrimage sites and threatened many more. Pilgrims and pilgrimage were a huge source of income.
And then there is the personal appeal of holy war. Like their Muslim brothers, Christians who died while fighting in the Crusades was guaranteed a place in heaven. Here is a huge buy in for your lowly peasant. When life sucks, and doesn’t look like it is going to get any better, then the idea of a afterlife upgrade looks that much better.
So, let go of the notion that Islam was the victim of the Crusades. If you pick a fight, don’t cry when your opponent opens a 900 years can of whoop ass on you.
As much as Christians and Muslims want to paint themselves as being peaceful and benevolent, neither can escape their history nor can they escape the greatest fact of all: they are human institutions and or movements and as such they have all the failings of the mortal coil.