Taylor Swift seems like a far better person than most billionaires, but the existence of billionaires itself is a moral failing, IMHO. I agree with xantoxis, if you're truly doing everything you can to help others, it's impossible to become a billionaire, because you'd never hoard that much resources when they can do so much good for so many others.
Look at someone like Dolly Parton, who would be a billionaire if she didn't give away so much money. She's doing it right.
Of course, Rowling, in addition to being a billionaire, is also a cruel, hateful creature, where Taylor is not AFAIK.