The sentiment that dominates all Rousseau’s works is a certain plebeian anger that excites him against every kind of superiority. The energetic submission of the wise man bends nobly under the indispensable empire of social distinctions, and never does be appear greater than when he bows; but Rousseau has nothing at all of this loftiness. Weak and surly, he spent his life spouting insults to the great, as he would have offered the same to the people if he had been born a great lord.
Source, in full
His character explains his political heresies; it is not the truth that inspires him, it is ill humour. Whenever he sees greatness and especially hereditary greatness, he fumes and loses his faculty of reason; this happens to him especially when he is talking about aristocratic government.
Notes from Wikiquote
p. 138