Full blown essay like answers are more than welcomed. What does the 'ruling class' gains from surveiling it's own population. What do they fear the most? What there is to lose, what there is to gain?
Optimistic perspective: Citizens are expected to sacrifice personal freedom for safety. The state watches out for bad actors so it can stop them before they cause harm.
Cynical perspective: Citizens are expected to follow a moral code or pledge loyalty to the state. The state watches out for deviants so they can be removed.