Great, you just accused him of being a communist and, ergo, an evil person. I think you might have skipped a step where you explain how his idea equals communism, which, as far as I know, has something to do with who owns the means of production.
You ask why J.K. Rowling should pay more than others for the books she sold. Well, she benefited more than others from the fact that there are such things as people who can read, for one, which is something that is supported by the state. The more you have, the more you take advantage of the things that society has to offer, such as infrastructure for transporting books, for example, and law enforcement for contracts and copyrights, and so on.
J.K. Rowling will not starve, ever, even if taxes for amounts over 1 million go to 80%. She would not have less money than the less successful authors, just her tax bill would be bigger, total percentage wise, than theirs.
Progressive taxation is not anti-capitalistic in any way. We can argue how steep the curve should be, but no tax loopholes at least should be something we all agree on.