I think especially in the digital age you could theoretically earn a billion dollars without exploiting anyone, like if you wrote an ebook or made a video game that pops off like Undertale, where there is little to no labor required for distribution. It's still unethical to hoard that much wealth and society should tax it away from you. Even if we were to accept the narrative that some billionaire celebrities made their wealth through ethical means (which they didn't), they still very much have the ability to give it to people who need it and choose not to.