I only read philosophy in the boudoir so I am far from an expert on De Sade, but in the book I cited above he took a long (and quite abrupt) detour to illustrat

I only read philosophy in the boudoir so I am far from an expert on De Sade, but in the book I cited above he took a long (and quite abrupt) detour to illustrate his ideas on "proper, rational" way to organize public life - it is actually an essay (written by one of the characters, and he takes a break from the sexual endeavours to read it to others) titled Frenchmen! One more effort to become real republicans. And his own version of "Philosophy" is part of the sexual initiation of one of the other characters. A girl who is a virgin, and has been raised in a traditional way and so, from the point of view of the other characters, has been fed lies for all her life.