VOLUNTEERS ARE A powerful force for good in the world. Millions give their time, effort and money to charitable causes such as feeding the poor, educating the uneducated, tending the sick and fighting for the dignity and rights of their fellow men, women and children. Today, doctors, dentists and nurses pay their own way to sail floating hospitals to places like Africa and Southeast Asia. They treat thousands of people in places where modern medicine is practically unknown. Former presidents and leaders of nations have picked up a trowel and hammer to build houses, AIDS clinics and roads and...