Most of the crusades were 'just wars' as ordained by the Pope. The Crusaders were doing God's work on Earth and in my mind, at least, it would make sense that they tried to represent him well. And I would also assume a greater proportion of Crusaders participated purely because they thought it was the right thing to do, like giving to the poor. I assume fewer fought because they wanted loot or the thrill or were just cruel. So I would imagine that this would lead to armies and commanders that would work harder to sin less. They would have fewer whores in the camps, they would not rape and pillage as much when they took towns, and they would keep alcohol consumption under control when compared to, say, contemporary Christian armies fighting Christians. Is there any truth to this?
Well you’re right that that was the ideal - they were supposed to be representing all of Christianity. It has sometimes been argued that the First Crusade was organized specifically to keep knights occupied, so they wouldn’t go around pillaging and killing each other and otherwise sinning at home in Europe. That’s a bit of an outdated argument these days, but it does reflect the medieval thinking that crusaders were supposed to be held to a higher standard than regular soldiers.
Calls for a crusade always included instructions about who could and couldn’t go. Children, the elderly, the sick, whole families were supposed to stay home - and especially women. Not just because women weren’t trained to fight, but because whenever there were women in an army, they were usually “camp followers”, i.e. prostitutes.
Of course it didn’t actually work that way at all. The leaders of the First Crusade agreed to punish soldiers caught with prostitutes. Some soldiers were probably caught and punished but there is a record of a monk and a prostitute being whipped.
On the Third Crusade there were prostitutes among the crusader armies as well. There is a bawdy song from the crusade about “laundry women” which is probably code for prostitutes.
On the Seventh Crusade a French knight was caught in a brothel, and was given the option of forfeiting his horse and armour and being expelled from the camp, or being led around the camp by the prostitute with a rope tied to his penis (he chose expulsion). There were also prostitutes in the camp when the crusade was in Egypt.
In the Kingdom of Jerusalem there were prostitutes as well. The Council of Nablus in 1120 established punishments for adultery prostitution. In the 13th century, the bishop of Acre Jacques de Vitry complained that the city of Acre was full of brothels and prostitutes.
Aside from prostitution, almost every crusade movement in Europe was followed by attacks on the Jewish communities. The massacres of the Jews along the Rhine during the First Crusade are well-known but there were also attacks in 1190, 1236, and 1251; I’m sure there were others but those spring to mind right away.
If you can excuse military actions as part of the “just war” theory, then we don’t need to mention the massacre at Jerusalem in 1099 or the cannibalism at the Siege of Ma’arrat...but both cases are surely examples of excessive violence that went beyond even what a normal non-crusading army might typically accomplish.
Sources:
James A. Brundage, "Prostitution, miscegenation and sexual purity in the First Crusade", in Crusade and Settlement, ed. P.W. Edbury (University College Cardiff Press, 1985)
Jay Rubenstein, “Cannibals and Crusaders”, in French Historical Studies, vol. 31, No. 4 (Fall, 2008)
Natasha R. Hodgson, Women, Crusading and the Holy Land in Historical Narrative (Boydell, 2007)
And some general sources for the First Crusade:
Thomas Asbridge, The First Crusade: A New History (Oxford University Press, 2004)
Jonathan Riley-Smith, The First Crusade and the Idea of Crusading (University of Pennsylvania Press, 1986)