I suppose The New York Times would not have printed this except for who the author is. If he believes what he's written, I trust he will allocate his Foundation's resources to radical political parties. (The increasing number of philosophers who seem to think charitable giving is an ethical imperative would do well to contemplate the issues raised by Mr. Buffett.)
UPDATE: A very apt comment on the piece by Dan Kervick:
A system in which liberals tolerate massive inequality, exploitation and structural dysfunction on the one hand, and then lobby rich people to "give back" in various ways - creative and sometimes effective though those give-backs might be - is an embrace of injustice and the prerogatives of power, not a challenge to it. Charity-state liberalism and the cult of philanthropy are neoliberal capitalism's way of defending itself against structural change while buying indulgences for its sins.