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.
Now, Christians; image that you are not a Christians and do not feel any grace, pity, love, heartbreak or even righteous anger, etc.
Now you understand why the groups mentioned above hate Christianity; they literally view us as devil worshippers.
How so?
Understand that what the devil does is to imitate that which YHVH does but backwards, inside out and upside down or, as some term it, same but opposite.
The secret doctrine of the aforementioned groups—all of them in some form or another—is that the true wise, good, God did not create the material realm but that it was a lesser god who did so.
This lesser god is viewed as evil because it created the material realm and matter is viewed as evil as it is far below the spiritual.
The God of the Bible, YHVH, is seen as this evil God and thus, Christians (and Jews) are views as worshipping this devil.
Into the picture comes a being that brings true enlightenment to humankind. This being also comes in many forms such as the serpent/satan in the Bible, Prometheus the titan in Greek mythology, etc.
Thus, the enlightener (who is actually the endarkener) is worshipped as the true god.
Thus, the call good evil and evil good and so they turn the one true living holy God YHVH into satan and satan into god and assign the worship of that god, the one whom they can be like, to themselves and the worship of the evil God YHVH to Christianity.