Do you give money to charity? You do if you're a typical American. More than 70 percent of US families contribute every year, and the average household gives at least $1,000. Charitable donations in America add up to about $300 billion annually — which is more, as Arthur C. Brooks of the American Enterprise Institute points out, than the entire gross national product of Finland, Portugal, or Peru. Americans give 12 times as much to charity each year as they spend on professional sports, and almost 30 times as much as they spend going to the movies. By any yardstick,...