One of the many problems I have with Christianity is its absolute intolerance for other religions or worldviews. Christians love to call atheists arrogant and smug etc. but in reality these are perfect descriptions of the christian spirit. The bible is chock full of prejudices based on what the authors believed to be their gods standards of morality. Have you ever noticed how these views reflect those of all views that are common to the middle eastern man? The bible clearly discriminates against women, gays, other religious beliefs, in the case of the O.T. all non Jews, and a slew of other things.
Christianity was founded on intolerance: this is evident from its original source of Judaism. When God supposedly called the Hebrews out of Egypt the first thing he had them do was to conquer the so called promised land and its inhabitants. And one of the first commands on every conquest was to destroy their temples and altars to heathen gods. After the christian church had the support and power of the Roman government they continued the tradition of eradicating any an all other religions that were not Christianity. When they ran out of religions to kill then they began establishing their own theology and began destroying other Christian groups who were not in agreement with their interpretations of the scriptures.
First Kings chapter 18 tells a horrendous story regarding Yaweh (God) and his intolerance for other religious beliefs. Not only this but it also demonstrates how the biblical deity ordered the murder of 450 men for serving as prophets to Baal. The people were given the chance to choose to serve God but the prophets were not. Jews and Christians have carried out this tradition throughout their entire history, yet some try to attribute all the crimes committed by the church not to God but to the men that committed them.
In reality, they are just following the precepts as taught in the scriptures which they believe to be the word of their deity. They are following the examples such as the one I have presented in the book of 1 Kings chapter 18. In the Old Testament it was okay to kill in gods name. The New Testament believers just kept those old traditions alive as they were establishing and building their theocratic empire. Seen in this context one can understand why Christians are so bigoted and intolerant to any an all things that do not fall in line with their prescribed belief system.
In the context of the crusades this same spirit of intolerance was used in a political manner as well. They used the power of the Roman Empire to destroy all those that opposed their teachings and views. In conclusion the Christians were doing what their biblical ancestors the Jews have been doing for thousands of years.