I think that many people don't get that a billionaire doesn't have to be evil or selfish to be a danger.
Look at, say, Dolly Parton. She made her money by shrewdly licensing her art. She gives her money away, offers support to communities, sends out heaps of books to kids, all the things we'd like a "good billionaire" to do. (She also has a damn fine PR person, but let's take the image as reality for the sake of discussion.)
But her efforts to revitalize neighborhoods turned into gentrification and made folks lose their homes. She learned better, sure, but one person having that much cash and leverage does a LOT of damage while learning.
She means well. But meaning is irrelevant. Only impact matters. It doesn't matter if Godzilla tiptoes, he's too damn big to go downtown.
We can't afford that.