They were all working-class Catholics. Only Catholicism produces that brand of "Satanism."
Also, as far as Christian rock concept LPs from this early 70s go, overlook Aphrodite's Child's 666 at your own peril.
https://www.loudersound.com/features/apocalypse-and-orgasm-the-crazy-story-of-aphrodites-child-666-vangeliss-cult-masterpiece