It would be about control, spreading so much fear in the people, that they never even think about being disobedient, or causing problems. This tactic has been used many times thru out history, the civil rights events of the 1960s are one good example, the cops and govt to some extent were sending a message to the entire black community everytime they publicly beat and killed someone who was protesting, being disobedient, etc.
If you spread enough fear thru the masses, people WILL eventually break down and automatically obey. Heck obedience experiments were even done in the 1970s, the results found we are are a very obedient people when it comes to punishment, torture, death, etc.