That is a different issue one could argue about. All this report is saying is that low top rates don't help growth but they give the rich a greater share of the pie. Whether that is right or wrong is a different issue.
I think we forget how lucky we are to be born in the US. If BIll Gates or Mitt Romney were born in Sri Lanka, I don't think they would be as successful no matter how hard they worked. They were as successful as they are partly because they were born in the USA. I don't think it is unfair for them to give a little of that back to the country that helped them make it in the first place.