Merriam-Webster offers these definitions of sadism: "the derivation of sexual gratification from the infliction of physical pain or humiliation on another person; delight in cruelty; [or] extreme cruelty." The adjective, "sadistic," is often given as a synonym for cruel, and the term has long been used to describe monsters like Dr. Joseph Mengele.
By virtue of his literary output, the Marquis de Sade lent his name to a variety of behaviors. The worst horrors in Juliette represent cruelty on steroids, and the major characters, including the eponymous heroine, are apparently without any redeeming vestiges of humanity. [The same can perhaps be said about some of the world's leaders today, but that argument must await another discussion!]
One point should be underscored, however. S/M (or sadomasochism) is consensual, while the excesses described by Sade or enacted by various historical figures are not. S/M can indeed be a truly beautiful, loving experience, as the scenes shared by Elena and Giovanni (and also Elena and Angela) demonstrate.
I have sought to differentiate between the sadist, the abuser, and the psychopath. If Music Be the Food of Love includes a Holocaust scene with a Nazi captain who is a true psychopath. Later volumes present an abuser and several criminal sociopaths. It is imperative that readers do not confuse their behavior with that of Giovanni and other loving "sadists" within this saga.