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Here we have a man who grew up in a family that was at best inadequate and who went through life serially friending and abusing benefactors. He lived, in fact, at the expense of others and never returned even the most elementary gratitude, instead choosing to revile his benefactors as being out to get him. (In his defense, he was probably at least somewhat paranoid.)
Normally such a man would be seen for what he was and reviled or at least laughed at. But Rousseau took his shortcomings and made them into virtues. If he was socially awkward, well then, the affectations of society must be wrong, and it was savages like him who were noble; if he was ungrateful, well, it was no less than should be expected of a genius forced to endure the presence of mere mortals.