What, exactly, is the morally indefensible thing that they have definitely done? If it's definitely there, you should be able to point out what it is.
As a first pass, you’ve accumulated all that money, thus you’ve actively or passively, knowingly or unknowingly, taken advantage of a perverse systemic bug that allows that sort of money to accumulate in any one person’s hands to begin with.
But point me at any given billionaire and I can provide more context-specific examples, sure.
Apple, for example, steals 30% of the money of anything you buy on your phone.