"The diversity of American giving," Bill Gates recently said, "is part of its beauty." It also has made the United States the most generous and successful nation in the world. Every day, millions of ordinary citizens volunteer in thousands of neighborhood organizations, schools and businesses, and church and youth groups across America. The uniquely American ethic of donating to charity is something that the liberals who are among the 38 billionaires understand, but that the rest of the Democratic Party is in danger of missing. If income equality were the answer, as big-government liberals believe, some of those billionaires would be writing extra checks to the U.S. Treasury. But they're not. I hope more liberal billionaires will follow the lead and sign up to give their fortunes to private charities. And I hope more liberal nonbillionaires follow as well.