Wealth doesn't appear out of nowhere.

It isn't zero sum either. I'm fairly certain Warren Buffet creates quite a lot of it. I'm also sure the marginal value of yet another school teacher pales in comparison to it.

The donation of a small sum of an accumulated fortune cannot create an impact equivalent to if that fortune in its entirety had been distributed in fairly paid labor.

My inner anthropologist from Jupiter is confused by this sentence, what is this "fair pay" thing. Please elaborate on it.

The donation of a small sum of an accumulated fortune cannot create an impact equivalent to if that fortune in its entirety had been distributed in fairly paid labor.

Assuming for the sake of argument that Warren Buffet is a vampire squid on the face of the world ... why not? You have humans routinely buying liquor and cigarettes instead of malaria nets for their own children, or wasting dollars on negative sum games like jostling for positional goods.

And to be avoid misunderstandings I do think you can make a good case that some people & institutions probably are vampire squids in the sense I used here.

The charities that billionaires tend to support also don't necessarily apply their spending in any semblance of efficiency, if they even affect good policy decisions with the impact they do have.

We aren't talking about what billionaires tend to support. We are using a thought experiment of primary school teacher vs. efficient charity donating rich dude to help you decide whether you where on the curve you want to go.

I'm pretty sure that being a pirate in Somalia and donating to efficient charity is probably justified by utilitarian calculations. If you can't possibly imagine this being the case, pause to consider that a criminal is just a start up government, a local bandit who ideally would want to have the monopoly on violence that a real state has but just isn't good enough for now. The best approach for the pirate would be to just stay in port and have passing ships pay him protection money. We accept some taxation of the trade routes can produce better results than not taxing it at all. I think it clear most government spending is much worse in its impact per dollar than efficient charity. If you disagree why in the world aren't you donating money to say the US government or writing up an argument for it? Model piracy by me and my merry armed band in Somalia as a tax on the trade route, then judge them as you would a government program with the same bang for buck.

To give another controversial example, I find it plausible that selling Marijuana and several other kinds of drugs (but not all) full time and donating the money to efficient charity beats out being a primary school teacher or working in kindergarten on utilitarian grounds.