Beyond the already presented arguments from the utilitarian perspectives and the perspective of active wealth accumulation that requires a lack of morals, I want to offer a perspective on the control that this much money gives you. Since a billion dollars, or even further, the billions of dollars that billionaires have are hard to imagine/visualize, here is a handy visualization which i urge you to scroll through. (you have to scroll to the right)

Now, beyond being simply astonishingly awful because of the amount of good those people choose not to do, it’s evil (I dont like the word in this context but I lack a better one) because of the control these people gain. Having billions of dollars is not just money in the sense you and I think about it. Its control, its capital. Simply through its absurd quantities it gains the emergent property of influencing millions and billions of peoples lifes, often in subtle ways like where factories are built or how resources are allocated, decisions that should by all means have democratic legitimization but are controlled by individuals like feudal lords.

And beyond that, this power influences elections through voters or through plain and simple corruption. But not the kind of small level nepotism we think of where a company wins a bid for some building, but corrpution on a level that influences state legislature and millions of people for decades to come.