The major difference between Locke and Rousseau's account of the state of nature is the reason for using it as a literary device.

For Locke, the state of nature has the capacity to become a state of war but it can also be a place of increased liberty for the individual. Locke was examining the reason for moving out of the state of nature and the creation of sovereign authority. He argued that the need to protect private property and create security, inspired people to sacrifice some of their liberty to create an original (or social) contract and place themselves under the sovereignty of a ruler. Importantly, in Locke's opinion the consent for this authority - or transaction of power - can be withdrawn if the monarch/ ruler acts in a tyrannical manner. This is because they would be placing people in a state of war and thereby forfeiting their authority. This argument was developed in relation to the absolutist ambitions of Charles II and James II, and had influence on the American Revolution.

For Rousseau, the state of nature enables him to examine human nature in its primitive condition. He undertakes this to attack the reductionist ideas of Hobbes and Mandeville, who strip man of God and claim that humans are animalistic and violent. According to Rousseau this is incorrect, as he believes that people have inherent (natural) virtue. Moreover, people live in accordance with nature, freely interacting and living together. He argues that private property is the beginning of humanity's ills, and creates arrogance and competition not present in the early state of nature. Such arrogance drives humanity to desire greater property while losing their national compassion. The only way to restrain this behaviour is to create a civil authority that restrains the negative behaviour people now engage in.

So while Locke would argue that people can behave badly, he is less interested in human nature and more concerned with the location of sovereign authority and consent, and how it is exercised. Rousseau is examining the problems in the human condition due to interaction, and how this created the inequality and aggression that caused the development of civil society - something he laments (which Locke does not).

I haven't written this, actually I have copied this article from a website. To me, it is a good answer to this question. I hope it helps.