How does Rousseau justify his arguments about equality?

Rousseau's arguments about equality are framed within his understanding of the Social Contract, the title of one of his best-known works and an idea of society organized around the concept of the "general will." Rousseau differs with Hobbes in his view of human nature, and sees primitive society, the "state of nature," as one where cooperation and harmony are prevalent.
This positive view of humanity challenges Hobbes' darker vision and becomes the foundation for Rousseau's ideas about equality and government. He suggests that inequality comes from existing social arrangements and hierarchy, and that an ideal, egalitarian society would be arranged around a social contract which emerges out of the "general will," in essence the good of the community and the welfare of the whole.
While some might suggest that Rousseau's "general will" runs contrary to individualism, challenging equality, this is no the case. For Rousseau, political power and the role of the sovereign is to secure the freedom and equality of a society's citizens, not limit them. In this respect his vision of government is one which only intervenes to create balance and harmony, not to directly rule. Because of a positive view of human nature, he suggests equality emerges out of the "general will" in a society stripped of previous inequalities.