The article explains <i>what</i> it is, but not <i>why</i> it's supposed to be good. Except perhaps that the proceeds of the tax could be used for welfare payments.<p>As explained at the bottom, such a tax is likely to cost holders of retirements account money.<p>A more important effect might be slowing the giant vacuum sucking bright technical people needed elsewhere into Wall Street. Bloomberg could help with that by not hiring so many himself.