Michael Kinsley has a wrong premise about capitalism. Its justification is not that it makes a contribution to society (though it does that) but that it respects each individual's right to his own life and the fruits of his efforts.
Anyone, rich or poor, who earns his money honestly has the right to use it as he wishes. No on else has a moral claim on it. No one has a right to say how much another person should earn if the money is earned through voluntary trade.
Seizing or limiting another person's wealth because he is judged to have too much is not social justice but exploitation.
Edwin A. Locke