I always found the "Children's Crusade" to the be the sadest. Thousands of kids from Central and Eastern Europe made it to somehwhere in Turkey and were captured and sold into slavery. The first example of that peculiarly western notion of "meaning well"; unintended consequences; and the triumph of reality over good intentions.
Sound familiar?
A pathetic current version is the "we never dreamed they would fire live bullets..."
Children I can understand; Adults acting like children...
The valiant duke Godfrey of Bouillon, the knights, and the other men of arms that were with him descended from the walls all armed into the town. They went together through the streets with their swords and spears in hand. All them that they met they slew and smote right down, men, women, and children, sparing none. There might no prayers nor crying of mercy avail. They slew so many in the streets that there were heaps of dead bodies, and one might not go nor pass but upon them that so lay dead. The men on foot went into other parts of the town in great bands, holding in their hands great poleaxes, swords, mallets and other weapons, slaying all the Turks that they could find, for they were the men of the world whom our men had greatest hate unto and gladliest would put to death. They were then come into the middle of the city. * * * I may not rehearse to you nor cannot the feats of every man by himself. But there was so much blood shed that the channels and gutters ran all with blood, and all the streets of the town were covered with dead men, in such a wise that it was great pity for to see, had it not been of the enemies of our Lord Jesus Christ.
Description of a Crusase by William of Tyre