The Crusades were not popular among the Christians of Europe, even if they were considered a military necessity as a counter-attack against the home base from which surprise attacks and invasions had been launched against sleepy and unsuspecting places like Spain, France, Hungary, Yugoslavia, and Austria.
During the Middle Ages while the Just War Theory - a debate about when or if a war was ever part of "justice" - was becoming more developed and Crusades were happening. Peace movements among Christians flourished. Francis of Assisi may or may not have been a pacifist, but he lived as if he were. A peace movement known as the "Great Alleluia" involving thousands of people took place in northern Italy in the 13th century, lead by an energetic priest who went from town to town, preaching in public. In 1233 the movement had grown to such proportions that 400,000 people gathered to demonstrate for peace and reconciliation. Another Italian peace movement known as the "Bianchi" moved about in thousands from city to city. Peacemaking was their major work. One chronicler notes that by the time one of these processions reached Rome its numbers had swelled to 200,000. Various groups of monks and priests opposed the Crusades, sometimes with words, and sometimes with actions.
Popular opposition to the Crusades spread, sometimes for these spiritual reasons, and sometimes for more worldly reasons: the Crusades cost money, and the soldiers who were part of them behaved like pagans. Yet the public tolerated these Crusades, even if they didn't like them, because it was understood that the alternative was a massive invasion by the Islamic armies into Europe.
People remembered how a Muslim army took over almost half of France, burning the wheatfields and houses, raping and killing the villagers, before Karl Martell and his army were able to turn them back. Those horrifying memories made the Crusades seem like a necessary, if unpleasant, defensive move.
