At Gorgias 492, tr. Helmbold, the ‘divine’ Plato puts the following words into the mouth of Callicles:
A man who is going to live a full life must allow his desires to
become as mighty as may be and never repress them. When his
passions have come to full maturity, he must be able to serve them
through his courage and intelligence and gratify every fleeting
desire as it comes into his heart.
[. . .]
The truth, which you claim to pursue, Socrates, is really this:
luxury, license, and liberty, when they have the upper hand, are
really virtue, and happiness as well; everything else is a set of
fine terms, man-made conventions, warped against nature, a pack of
stuff and nonsense!
Now let us consider what the decidedly undivine Marquis de Sade has Mme. Delbene say in Julliette or Vice Amply Rewarded:
. . . I am going to dismiss this equally absurd and childish obligation which enjoins us not to do unto others that which unto us we would not have done. It is the precise contrary Nature recommends, since Nature's single precept is to enjoy oneself, at the expense of no matter whom. But at our leisure we shall return to these subjects; for the nonce, let's now put our theories into practice and, after having demonstrated that you can do everything without committing a crime, let's commit a villainy or two to convince ourselves that everything can be done. (p. 30, emphasis in original, tr. Casavini)
From the cover: "abridged but unexpurgated from the original five-volume work especially for the adult reader." In other other words, the good stuff, i.e., the philosophy, has been cut, but the 'adult matter' remains. This use of 'adult' evokes a smile — but that's another post.
The natural man, in the grip of his lusts, is a natural sophist: what can be done is eo ipso permissible to do. Reason in a philosopher without God easily becomes unhinged.