Nietzsche does indeed enact a 'transmutation of all values', yet not in order to elevate the value of evil.
It is rather a matter of transcending the dichotomy of good and evil, rising 'beyond good and evil'. He ascribes no inherent meaning to these two concepts beyond their being symptoms of a certain physiological constitution. For Nietzsche, to reject morality is not to choose evil over good; anyone who does so remains trapped within the moral framework that upholds the opposition between good and evil—still confined by its constructs.
The superhuman is one who surpasses this framework altogether, embracing neither side of the moral dichotomy but existing 'elsewhere'; he is not 'immoral' but 'a-moral'.

Sade, on the other hand, comes closer to the notion of immorality we are seeking to examine. The audacious passages in Sade's works, and the seductive danger radiating from Philosophy in the Bedroom, long consigned his writings to the hidden shelves of libraries. Here we seem nearest to an axiological stance that assigns supreme value to evil. Yet Sade, perhaps with deliberate mischief, chooses instead to argue the opposite. While he exalts destruction and cruelty, he does so not to glorify crime but to deny that such acts constitute crimes at all: Destruction being one of the chief laws of Nature, nothing that destroys can be criminal; how might an action which so well serves Nature ever be outrageous to her? ¹.

In his rhetorical manoeuvring, Sade does not question the value of virtue itself but redefines its essence; true virtue, he claims, lies in cruelty, not pity: Cruelty, very far from being a vice, is the first sentiment Nature injects in us all. Cruelty is simply the energy in a man civilization has not yet altogether corrupted: therefore it is a virtue, not a vice ².

Further, condemning human pride much as a Church Father might, Sade reaches the astonishing conclusion that murder is legitimate: Tis our pride prompts us to elevate murder into crime. Esteeming ourselves the foremost of the universe's creatures, we have stupidly imagined that every hurt this sublime creature endures must perforce be an enormity; we have believed Nature would perish should our marvelous species chance to be blotted out of existence ³.

Moreover, Sade upholds the foundational structure of morality by appealing to a legitimising principle—not God, but Nature. He observes, for instance, that Women are not made for one single man; 'tis for men at large Nature created them, and urges them accordingly: Listening only to this sacred voice, let them surrender themselves, indifferently, to all who want them ⁴.
Evil is therefore not self-justifying; it is not embraced for its own sake. Nature legitimises evil just as God once legitimised good, and this legitimisation effectively reclassifies evil as good. The object of affection is not evil itself but Nature, which one pursues through acts conventionally deemed evil. Sade does not engage in evil because it is evil but because it is natural.

Ultimately, rather than affirming the value of evil, Sade seems to make it vanish—much as classical theodicies do. Eugénie, for instance, exclaims in response to Dolmancé's endorsement of incest: Oh! My divine teachers, I see full well that, according to your doctrine, there are very few crimes in the world, and that we may peacefully follow the bent of all our desires, however singular they may appear to fools ⁵.
To which Dolmancé replies: There is crime in nothing, dear girl, regardless of what it be: the most monstrous of deeds has, does it not, an auspicious aspect? […] Well, as of this moment, it loses every aspect of crime; for, in order that what serves one by harming another be a crime, one should first have to demonstrate that the injured person is more important, more precious to Nature than the person who performs the injury and serves her; now, all individuals being of uniform importance in her eyes, 'tis impossible that she have a predilection for some one among them; hence, the deed that serves one person by causing suffering to another is of perfect indifference to Nature ⁶.

Sade thus appears to deny the existence of evil rather than to glorify it. The behaviours he extols—cruelty and debauchery—are redefined not as evil or vice but as virtue, properly understood.

We might nonetheless ask whether Sade deserves to be taken seriously as a thinker, and whether texts that may have been intended to mock serious moral discourse merit earnest analysis. We should be wary of mistaking irony for a consistent doctrine.

These ideas are specific to Philosophy in the Bedroom, whereas in The 120 Days of Sodom characters embrace evil for its own sake, recognising it as vice rather than as misunderstood virtue. Here, the pleasure derived from evil is held to be the supreme value: [These principles] have made me understand the emptiness and nullity of virtue; I hate virtue, and never will I be seen resorting to it. They have persuaded me that through vice alone is man capable of experiencing this moral and physical vibration which is the source of the most delicious voluptuousness; so I give myself over to vice ⁷.
It should be noted once more, however, that nature serves as the legitimising principle: These instincts were given me by Nature, and it would be to irritate her were I to resist them; if she gave me bad ones, that is because they were necessary to her designs ⁸.

In conclusion, it bears repeating that extreme axiological positions are rare in literature and philosophy alike—whether the love of evil for its own sake, 'radical evil', nihilism, or eclecticism. Far from discrediting these doctrines, this rarity only underscores their truly extraordinary character.

1. Philosophy in the bedroom, p. 433
2. Ibid., p.449
3. Ibid., p.434
4. Ibid., p. 481
5. Ibid., p. 433
6. Ibid., p.478
7. The 120 Days of Sodom, p.26
8. Ibid., p.27