The example was between treating HIV and malaria. A person infected with HIV might cost $100,000, while a person dying of malaria might only cost $1,000 to cure. Since we can help 100 people with malaria for every one with HIV, shouldn't we focus first on malaria, and only turn to HIV once we've helped everyone we can with malaria?
The logic is sound, but try telling that to a doctor working on HIV (let alone a patient with HIV). But how else could we decide?
The big idea seems to be to add up the (monetary) costs of charities and look at some simple metric (like lives saved) to pick and choose the best charities.(link to bjorn lomberg's thinktank) But do we only care about a single metric, a single value? And how compare education to disease, senile dementia to juvenile delinquency?
The same problems bedevil conservation...
I think the simple answer is that there are no simple answers, and every approach has a place. If some government minister will only listen to economic arguments, use them... but others will listen to other values, and those also matter. Whether people care about the scariest diseases (terminal diarhea) or the cuddliest endangered animals (link to cockapo), these interests are meaningful.
There is a long tradition in decision science and economics of critiquing irrational human preoccupation with infrequent, but salient/scary crises (link to risk diagram disasters axis) as opposed to rational actors (link to behavioral economics discussion, maybe wikipedia) dispassionately evaluating statistics. I try to avoid news sources because of our (link) well-demonstrated cognitive biases, but I don't think we can (or should) "fix" every element of human thinking.
Yes, every decision is a choice to focus on one priority over another, and yes it is not rational to make that decision without comparing and ranking all choices. But pure rationality doesn't take account of the full richness of human life. We care about many values, not just The Most Important. Is it absurd to try to save endangered species when many people don't have adequate nutrition? (link to weird conservation stories, nature conservancy).