Hereinafter the “they” in the question “Why do they hate Christianity?” refers to what is variously termed secret societies, mystery religions, cults, occults, magickians—by any other name.
Imagine someone, or rather a very large group of people, who literally worship the devil, teach their children to do likewise, systematize this worship into a hierarchic authoritarian religious structure, fund people to travel the world in order to convert them to devil worship, etc., etc., etc.