Amazon founder Jeff Bezos changed how people shop.REUTERS/Abhishek N. ChinnappaBillionaires are sometimes criticized for having excessive wealth and for fueling gross inequality.Two professors say the uber-wealthy should be celebrated for improving people's lives in many cases.Billionaires fuel growth through innovation, and raising their taxes could backfire, they told BI.Critics denounce billionaires as greedy and corrupt, bemoan their existence as evidence the system has failed, and blame them for many of the world's ills.