Think in terms of a legal contract. If we make an agreement and I don't hold up my end, you have every reason to no longer hold up your end. No obligation remains. The idea of the Social Contract is that the government rules by consent of the governed. To validate that consent, the government must work for the protection and well-being of its people. As long as it does, the people are obligated to follow the laws and accept its form of civilization. All of this implies that, once the government no longer works for the people, then they have no obligation to allow themselves to be governed. They have every right in the world to revolt, in effect declaring their consent to be governed null and void.