At the end of the book he attributes a paraphrased quote to Jean-Jaques Rousseau:
The communistic republic of Plato involved slavery; that of Lycurgus employed Helots, whose duty it was to produce for their masters, thus enabling the latter to devote themselves exclusively to athletic sports and to war. Even J. J. Rousseau—confounding communism and equality—has said somewhere that, without slavery, he did not think equality of conditions possible.
Did J.J. Rousseau really say slavery was a necessary condition to reach equality of conditions?
Post Scriptum : I already asked this very question on another StackExchange site without luck : on Skeptics