You are equating morality with https://en.wikipedia.org/wiki/Utilitarianism. With "optimizing the integral of happiness"

You can be a perfectly moral denteologian (that is, a person that believes in moral rules, not in moral objective functions) and be a billionaire.

A second possibility: you can be a utilitarian, and believe that positive sum trades should always be taken (untenable position as this is (1)) and think you are taking one such trade. That is the claim Elon Musk seems to be making: This money today will save human lifes (electric cars reducing climate change) and increase the future number of lifes worth living in the cosmos (spacex)

(1) On the untenability and self-destructiveness of "always take positive sum choices, even if they harm you"

1) living an American middle class life while children starve might be similarly morally reprehensible

2) Not killing oneself and donating ones organs (saves what? 10 lives?) might be similarly morally reprehensible

>since wealth has diminishing marginal utility, wealth transfer programs are inherently positive-sum -- and thus, accumulation of wealth so far beyond human need is negative-sum.

Retort from first year philosophy: "if this is the case, why aren't you donating most of your disposable to starving kids in africa? Surely that would have higher utility than buying yourself an iphone or macbook?"

How do you know (a) that they have disposable [sic], and (b) that they aren't donating most of it?

> since wealth has diminishing marginal utility, wealth transfer programs are inherently positive-sum -- and thus, accumulation of wealth so far beyond human need is negative-sum.

Is this really the case? The wealth of most millionaires is probably mostly in bank accounts, but only once you have hundreds of millions to billions of dollars in one place are you able to coordinate megaprojects: space travel, vaccine manufacture, clean transport, chip fabs, Stuxnet...

Since billionaires get that way by being better at investing, the theory that poor people inherently put money to better use is not persuasive.

> Since billionaires get that way by being better at investing, the theory that poor people inherently put money to better use is not persuasive.

The claim is that poor people’s use is better for society (positive externalities) not for the poor person. That billionaires are better at assuring that any negative impacts of their transactions are externalized, and insuring internalized gains, is clear, but not the point.

> for society

How do you know this is better than the billionaire providing a service to society that's so valuable, it made him a billionaire?

> How do you know this is better

I don’t, and I’m not making the claim that it is.

I’m saying that the fact that billionaires get to be billionaires by a combination of ability and inclination at maximizing their personal benefits from transactions, while true, doesn’t provide even slight counterevidence to the claim it was offered to rebut.