Believe it not, this is what you are up against.

Good luck.

Many don't know that the first Catholic crusade was into France to kill the Cathar's. 1209

What did they believe that was not acceptable to the Catholic Church?

Cathars believed that the good God was the God of the New Testament, creator of the spiritual realm, whereas the evil God was the God of the Old Testament, creator of the physical world whom many Cathars identified as Satan. Cathars believed human spirits were the sexless spirits of angels trapped in the material realm of the evil god, destined to be reincarnated until they achieved salvation through the consolamentum, a form of baptism performed when death is imminent, when they would return to the good God as "Perfect".