I have a fairly strong intuition that “if you don’t fund it, somebody else will” is more true than “if you don’t do it, somebody else will” so that this counter-consideration is outweighed. It’s important to note that many projects of high social value are the first of their kind, and that finding somebody else to execute such a project is highly nontrivial. I think that it’s also relevant that 114 billionaires have signed the Giving Pledge, committing to giving 50+% of their wealth away in their lifetimes.

On the other hand, the vast majority of people who want to do good in the world try to "do it" rather than "fund it" (hence why "Earning to Give" is considered a novel, controversial idea), which makes me think that “if you don’t do it, somebody else will” is more true than “if you don’t fund it, somebody else will”. Convincing other people to donate as much as you would have done in an EtG career is also highly nontrivial. And I think that those Giving Pledge stats are about as relevant as the fact that the nonprofit sector employs about 10 million people in the US.

(Still very glad to see this post on LW though, lest any of us should forget that Will's article, and probably many of the articles discussing EtG, were written for audiences quite different from LW! I especially liked the sections on Discrepancy in Earnings and Replaceability.)