The argument against billionaires being “no one needs that much” or “a billion is too much money for someone to have” is really missing a point. People who have a billion dollars do not simply behave as consumers but as investors and/or corporate leaders (entrepreneurs included).
What that means is: they having a billion or more dollars to invest or manage is capitalism’s governance system: those which invest wisely keep (or expand) their responsibility to invest (more funds) wisely. In a sense they get a greater vote on the economic decisions of the society as a whole. They may decide to invest in IoT, or space travel, or frozen yogurt, or shale gas. But together they act not as consumers, but as the economic decision making system of society.
Take their billions away, and where does that governance go?