Amid a historic crisis, billionaires are keeping their money to themselves. : For years, wealthy Americans have argued that philanthropy was essential to a functioning society. In contrast to unwieldy, inefficient government programs, private donors have the ability to take swift action and deliver social impact free of bureaucracy. “My wife and I set up a foundation about 20 years ago,” computer magnate Michael Dell said last year in response to a Democratic proposal to enact a wealth tax.