I supplied in another post several examples of what radical Christians thought justified their actions. Later Christians have rebuked such interpretations, but what happened, happened.
And your insistence on excluding the Old Testament from this is strange to me; if the Christians don't want it to be used, then why print it in their Bibles? If the Old Testament was good enough for Jesus and Paul to quote, and for apparently all later Christians except yourself, then why is it no surprise Crusaders did? Or is it that Christianity is just a religion of peace, while Judaism is a bloody, hateful religion, founded on a book that teaches so many violent things - the presence of which apparently even you acknowledge?
Well for one, both Jesus and Paul were Jews. Is it any wonder that they would quote from the Jewish Old Testament?
Christians of today do not follow the rules set out in the Old Testament, be it prohibitions on eating certain foods, instructions on how to sacrifice live animals on an alter, or exhortations to kill Philistines.
When asked which of the commandments was the greatest Christ says "Love God with all your heart, and all your soul, and all your mind, and all your strength. Second, love your neighbor as you love yourself...." Part of Christ's mission was to bring us face to face with our shortcomings and bloodlust (i.e., our old "sinful" rebellious nature) so that we could move beyond it.
Where in Islam is the message of mercy and forgiveness and love (for Jews and Christians as well as other Muslims)? Yes, the Old Testament is full of violence and murder, and Christ teaches us that we do not have to be a slave to what the past has given us.
If the history of Judaism, Christianity, and Islam are less than exemplary then by all means blame men. But only one of these religions explicitly teaches us to do good to all that hate us. One of the other religions explicitly tells its adherents to kill others with whom they disagree.