Thanks. Side note (I posted another comment about this just now, because it just clicked for me this morning): I think Ben Hoffman thinks (or thought, when he wrote his blog posts) that when you treat more malaria cases or do other philanthropy, marginal cost goes down. He says:
If we assume that all of this is treatable at current cost per life saved numbers—the most generous possible assumption for the claim that there’s a funding gap
When in fact it’s the least generous, under the assumption that marginal cost goes up. If you think marginal costs will only go down from current levels as we scale, then it is indeed suspicious that nobody’s decided to just dump all their money into scaling.
Retracted, because after conversation on Ben’s blog, it’s not a matter of thinking marginal costs will go down with scale—rather, he treats “funding gap” more strictly than I would, something like “the amount of money charities can absorb and deploy at approximately present marginal costs per life saved”. And if you define the funding gap as “the amount of money that can be deployed at approximately present marginal costs, or better”, then “assume marginal cost does not go down at all” is indeed the most generous assumption.