This is from Paul Krugman’s Playboy Interview:
Bill Gates Sr used to say this: suppose you were given the choice of being born in America or in Ethiopia. What proportion of your eventual fortune would you be willing to give to be born in America? Given the great good fortune of getting to live and run a business in this country that has all the advantages an advanced country with a decent system provides, how can you think it’s all you? And then, how can you feel you don’t have any obligation to pay it back?