Permanence.
Having a large slave population is highly profitable. The downside to a large slave population is if they decide to be free they can typically free themselves and kill their masters if they want it bad enough. With machines and some AI you can automate everything and dispose of your slaves as they're obsolete.
Short answer, yes.
Long answer
TLDR, they believe their God, Lucifer, is the one true God and Christianity which takes bread and wine as the body and blood to be a perversion. Obviously IDK how prevalent the actual practice is, but Hollywood loonies larp cannibalism quite often and also there's the adrenochrome thing which others have mentioned.