“It is true that the higher men can climb by the use of their knowledge, the lower they can fall through its misuse. It is up to us to put our growing knowledge to good use. For unless we all remember, at home and in our thinking about distant people, to treat them as we wish to be treated ourselves, all our plans for fun and happiness, all the beauty and fine freedom and hope of our lives, may be darkened by shadows that cover the world.”