“An education is truly “fitted for freedom” only if it is such as to produce free citizens, citizens who are free not because of wealth or birth, but because they can call their minds their own. Male and female, slave-born and freeborn, rich and poor, they have looked into themselves and developed the ability to separate mere habit and convention from what they can defend by argument. They have ownership of their own thought and speech, and this imparts to them a dignity that is far beyond the outer dignity of class and rank.”