Rousseau was genuinely revolutionary in the way in which he overturned the notion of Original Sin. For most thinkers before him the question was how Man was to be made good, given his bad or imperfect nature; for Rousseau the question was how Man became bad, given his natural goodness (his answer was society). He did not believe in a return to Nature, exactly, but sought the political means to restore Man to his natural goodness. Personally, I think Rousseau was disastrously mistaken in this; in my opinion, the limitation of the bad in Man is infinitely more important and less sinister politically than the search for the good. When you have limited the bad, the good can take care of itself.
 
Rousseau was also the unwitting founder of the psychology of the Real Me, that is to say of the inner core of each of us that remains immaculate and without sin, however the external person actually behaves. The inner core, the Real Me, is good; what might be called the Epiphenomenal Me, that is to say the one that loses his temper, tells lies, eats too much, etc, is the result of external influences upon him. In this way a monster of depravity may preserve a high opinion of himself and continue his depravity; nothing he can do can deprive him of the natural goodness first espied by Rousseau.
 
Jean-Jacques was also, in his way, the philosophical progenitor of Facebook, of the notion that we should live our lives in the open, hiding nothing, for concealment is both the symptom and the cause of insincerity, which was one of J-J’s bugbears. He begins his Confessions in a self-congratulatory way: “Here is the only portrait of a man, painted exactly after nature and in all her truth, that exists and probably ever will exist.”