The article explains what it is, but not why it's supposed to be good. Except perhaps that the proceeds of the tax could be used for welfare payments.

As explained at the bottom, such a tax is likely to cost holders of retirements account money.

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.

How is this ‘Mike Bloomberg’s’ and not ‘Bernie Sanders’? Bernie had it in his manifesto before Bloomberg adopted it.