I really don't have a major issue with billionaires. If you are smart or lucky enough to invent the little umbrella on a cocktail that makes a dollar per sale, if you sell a million of them you're a millionaire. Now invest the profit and work on your next invention. There's nothing voodoo or evil about it. It does generally take money to make money though.
If you have money, through a product, job, inheritance or whatever and invest wisely you can make a fortune. If you create a cultural game-changer company like Microsoft or are a brilliant investor like Warren Buffett you probably deserve to be a billionaire.
I do agree though that a lot of times (even with Bill Gates) these guys have to do questionable things to keep building the wealth. Change the laws if they're doing anything too egregious. Some of them seem fine like Mark Cuban. And fuck the assholes who don't give a shit how much damage they do to society in pursuit of more wealth (Murdoch, Koch Brothers, Thiel, etc.)