From his first:
Rousseau was the first great philosophic critic of what we call the Enlightenment, without being a defender of the ancien régime. Right from the start, he was seen by his critics as a mad father of mad fantasies. The leading philosophers of the French Enlightenment treated their former friend and colleague as a deranged traitor. He was seriously persecuted by governments and clergymen in both Catholic and Protestant parts of Europe, and celebrated after his death by those who made the French Revolution.And from his second:
Political conservatives, whether of a classical liberal or traditionalist orientation, have generally found Rousseau repulsive and dangerous, and his admirers tend to be on the political left. One striking exception to this generalization is Alexis de Tocqueville, who said that Rousseau was a man (along with Montesquieu and Pascal) with whom he spent time every day.
The deepest root of Jean-Jacques Rousseau’s opposition to Enlightenment political thought can be traced to his views on the state of nature, which are set out most openly in his “Discourse on Inequality.” For modern social contract thinkers such Thomas Hobbes and John Locke, the state of nature is the condition in which people like us find themselves before governments are instituted or where they have stopped operating. Rousseau believed this was extremely misleading because it assumes that what we are now we are by nature.A bit on terminology: The way I understand it, Hobbes, Locke and Rousseau were three greatly influential thinkers of the Enlightenment. They were "moderns." Nietzsche was not a modern. Rather he started post-modernity. H, L & R each were also united by the discursive theory of "state of nature," social contract and rights. But each also had profoundly different visions of that common ground.
For Rousseau, the nature of man is not an observable phenomenon. Instead, it is something that lies hidden beneath layers of characteristics acquired through our social lives, including the most important of all social institutions, human speech. The true state of nature is the condition men were in before being shaped by social life into the strange and unique animal that we are.
America's founding was Lockean. The big bureaucratic state as it currently exists is Hobbesian. And to the extent that Rousseau engaged in an egalitarian critique of Hobbes and Locke, the way the state currently redistributes wealth and provides safety nets can be credited to his vision (and the earlier Anglo-republicans like Harrington).