OK, so if one of the Galtian Ubermensch creates, say, a great manufacturing empire, who are we as a society to try to take away most of the money he makes through taxes? It's HIS.
(I can almost get this, aside from the fact that he didn't make "his" money without a lot of help from people who don't belong to his country club -- that would be US -- and from infrastructure and institutions our meager taxes helped build.)
On the other hand, it is immoral for those not working to take money from society that they did not earn -- through unemployment, food stamps, or Welfare. Parasites.
So - and here is where it breaks down - how do you then oppose the Estate Tax? If Galt dies, it's not his money any more, and his children/heirs HAVE NOT EARNED IT. Can't have parasites loafing around the country club, can we?