What people mean by "you can't earn a billion dollar" is that there's no work that's useful enough, alone, to be worth that much in reward. How can we live in a world where a moron can have a trillion to their name, while others work arduous physical labor all their lives and end up with nothing?

You might not believe you've done anything "bad" to become a billionaire, but the mere fact that you accumumated so much wealth necessarily means others, somewhere, had to work for it. The mere existence of billionaires is the mark of an unhealthy economy, that doesn't distribute wealth in an efficient or fair manner.