I think most of them earned their money through hard work, and it would be a dickmove to say "Alright, you've got too much so please give us (the government) a big part of your cake." I think there's not a single billionaire, who is publicly known, that does'nt know that with great money there's great responsibility. That's why they give dozens of millions of dollars to charity. They are builders, they create jobs, they create value (not exclusively billionaires, but entrepreneurs in general). If we would'nt allow them to exist, we would be 1 step closer to communism / hardcore socialism and I don't want that to happen..