In his The Social Contract, Rousseau talks of living in freedom in a 'state of nature,' that is, enjoying the physical freedom of having no restraints on our behavior, which would suggest that he would agree with John's killing of the old man (Sparknotes). Rousseau was trying to find a way in which man could come together with others and submit to their rules without losing his own freedom and power (Halsall). He says that by entering into a social contract, we place restraints on our behavior which make it possible to live in a community, but by giving up our physical freedom, we gain the civil freedom of being able to think rationally (Sparknotes). This means we can restrain our impulses and desires and learn to think morally. Morality, said Rousseau, only has meaning inside a civil society.
The social contract can be reduced to one single stipulation - that the individual alienates himself totally to the whole community together with all his rights (Halsall). Conditions will be the same for everyone when each individual gives himself totally, and no one will want to make the condition of shared equality worse for others. Once people are united in this way, an offense against one member is an offense against the body politic. If one person is injured, everyone feels it, therefore John would be condemned for his act.
This kind of society, with its morality and restraints on desires and impulses would never permit John to kill the old man and take over leadership