Yes, we see this all as crazy, but breaking yourself out of brainwashing is very difficult and rarely happens instantaneously. Human brains are so good at justifying our actions it's frightening. Just as any religious fanatic believes they are doing God's will, our brains contrive a scriptural basis for these things, just as
@CSIDreamer pointed out their zombies is just another word for demonic possession. Some who disagree with Christianity call Jesus a zombie. And in The Book of Mormon an incapacitated drunk is murdered and justified by the scripture 1 Nephi 4:13 "Behold the Lord
slayeth the
wicked to bring forth his righteous purposes. It is
better that one man should perish than that a nation should dwindle and perish in
unbelief." Lori said she would murder Charles if he got in the way of her mission--in her mind, slaying the wicked to bring forth God's righteous purpose. The same is true with the crusades, with suicide bombers, with witch hunts, you name it. A crazy person can justify themselves with any religious beliefs, and unfortunately, setting yourself right again requires adjustments in your reality, which is an incredibly painful and ongoing process.
I think I'm one of the few who thinks CD and LVD genuinely believe what they were peddling. Or, at least, allowed themselves to believe in this fantasy they fueled in each other. I don't think it makes them insane, just believers in their own incredibly destructive religious offshoot.
All MOO.
ETA: I'm actually a little terrified by how sympathetic MG still feels towards them. But then the abused often love their abusers. I'm absolutely not trying to deflect responsibility from these people, just pointing out it's a very tangled situation.