Fortunately also many knights joined the crusades. Some of them were sons of minor nobles looking for glory, some were younger sons without lands to herit and some went for the plain believe in their righteouness. Then there were Hospitallers and Templars who as partially monks, believed in their unstoppable power and justice. Templars at least were elite soldiers who left everything behind to fight for the god, needless to say they were very cruel and feared in muslims eyes, yet at the same time admired and honored in Christian eyes. Of course Christian people, the masses, thought that crusades were very just, what else could they believe, there was no-one to tell otherwise.