The Crusaders were Christians in many cases. Some where there for glory, battle, riches, etc. but many were there to defend their faith. If you go back to the history before the Crusades and look into what happened to many Christians making pilgrimages to the Holy Lands you may find one of the key catalysts admist all the other socio-political factors. History is up to the interpreter.
You can't apply modern, moral relevance to the past, the view, perspective and circumstances define how they interpreted their faith in the context of their time. I would say many who profess to be Christian are not IMO, but not my place to judge...I'm sure others would state I'm not Christian.
To know what you must believe as a Catholic, you should read the Dogma. You either accept it in its entirety, or you are not Catholic irrespective of what your novus ordo priest may say. IMO. YMMV