As noted in my last post, what I'm saying is that the problem here isn't that income inequality EXISTS -- i.e., is greater than zero. The problem is that, over the past 30 years, it has grown enormously. The richest people now take a much GREATER share of the nation's income than they did in 1980. That they take a disproportionate share is only another way of saying that they're rich, but the problem is how much they do, and how much more that is than it used to be.
There is a wide range of behaviors and circumstances behind where one falls on the economic scale. All else being equal (which it isn't), more effective economic behavior will net one a higher income. That's the reason why income inequality EXISTS. But over the past 30 years, economic behavior that used to result in a middle-class income has changed to resulting in a lower-class income, while economic behavior that used to result in merely being rich has changed to resulting in being mega-rich.
The bar of success has gotten higher, as have the rewards for the highest levels of success. The question that needs answering is why that has happened -- not the much simpler and less significant question of why there is any income inequality at all.