I'm as pro-capitalist, pro-democracy, pro-make-a-fuck-ton-of-money as you can get... But even I am blown away by the wealth of some of the top billionaires.
Just think about the good that some of that could do for the country. Put it into science. Put it into social welfare systems. I don't care, put it into something!
I don't know what the solution is. The naive comment would be if you make above X billion everything else goes to some re-distribution fund... Obviously that will turn a lot of people off. But the point is, I just don't think anybody needs that kind of wealth.