There are two ways to take control of others. Huxley and Orwell. Two methods in which a distopian future can happen / is already happening.
Orwell. As in George Orwell. Author of the book "Nineteen Eighty-Four".
In this, life is a world of perpetual war, pervasive government surveillance, and incessant public mind control.
The perpetual war keeps people busy producing things for the war. Keeping them busy means no time to think about things like freedom and free though. Government surveillance via telescreen (transceiving television) in every room. If you try anything you'll be disappered. Mind control by controlling and removing words from the language. Words like freedom, rebellion, privacy. If you can't name it then you don't know whats missing.
They don't know the truth because they can't get the truth.
The other way is Huxley. As in Aldous Huxley. Author of the book "Brave New World".
All citizens are conditioned from birth to value consumption. People take a drug called 'soma' to get comfort when stressed for example. Sex is encouraged at an early age for fun and as a social activity rather than to start a family. Things like marriage, natural birth, parenthood, and pregnancy - heck even family, don't exist in this world. No family, no mourning in case of death. If something bad were to happen then to solution is always more soma. Everything is all happy.
They don't know the truth because they don't care about the truth.
Pic related: http://fatpita.net/?i=1952