the statement "Kant is Sade" is the "infinite judgement" of modern ethics, positing the sign of equation between the two radical opposites, i.e. asserting that the sublime disinterested ethical attitude is somehow identical to, or overlaps with, the unrestrained indulgence in pleasurable violence. A lot-everything, perhaps-is at stake here: is there a line from Kantian formalist ethics to the cold-blooded Auschwitz killing machine? Are concentration camps and killing and genocides as a neutral business the inherent outcome of the enlightened insistence on the autonomy of Reason? Is there at least a legitimate lineage from Sade to Fascist torturing, as is implied by Pasolini's film version of Saló, which transposes it into the dark days of Mussolini's Saló republic? Lacan developed this link first in his Seminar on The Ethics of Psychoanalysis (1958-59), and then in the Écrits "Kant with Sade" of 1963.
Slavoj Zizek, Kant and Sade: the Ideal Couple