These atrocities are always - I repeat - always the result of attempts to engineer the "greater good" in human society. No one ever perpetrated one of these horrors who did not have the best of intentions. Hitler was trying to purify the human race and purge evil elements from the gene pool leading to the rise of perfect men and women (heroic, wise and superhuman). Lenin, Stalin, Mao murdered tens-of-millions to bring about a proletarian paradise where all will live in the midst of plenty in peace and harmony. Pol Pot and his henchmen simply implemented immediately those policies that were designed to transform their society into an agrarian eden of happy, thriving peasants living in harmony with the land and with one another never wanting for anything.
There are plenty of people around who have vast ambitions to enhance the human race and create a new eden for all. I think it was Thoreau who wrote that if he new a man was coming to his house with the sole intention of doing nothing but good for him he would run screaming out the back door in an effort to escape.
The "Good Post" reply was meant for you. I just noticed I posted that to myself. My wife's right, I do talk to myself.