Same question.
Natural means. Peace is not a goal by itself. A people who are forced to be peaceful hold chaos in their hearts and unleash it where it cannot be seen. They become crafty and cunning and even more cruel. What is more, the definition of peace that is enforced cannot be objective. The laws cannot be proven right.
In a society where peace is created at gun point, who is pointing guns at those who point the guns? The cruelest of people will seek out the job of pointing the gun.
The dictator is but one man. He cannot reign in evil. The same people who would take the position of the gun pointers will take the place of the dictator's enforcers.
If brainwashed completely, people lose autonomy. People without autonomy cannot help you grow. They lose their organic qualities. A clockwork orange is a horrible thing.