Gianfranco Pellegrino has written an interesting essay arguing that effective altruism leads to what he calls the Altruistic Repugnant Conclusion. In this post, I will provide a brief version of his argument and then note one possible response.
Pellegrino beings by identifying the following as the core tenet of effective altruism:
"Effective Altruist Maximization (AM): We ought to do the most good we can, maximizing the impact of donating to charities on the margin and counterfactually —which means that among the available charities, the one that is most effective on the margin should be chosen" (2).
He next argues that this core tenet can best be articulated as the following principle:
"Doing the most good amounts to bringing about the greatest benefit to the greatest number" with "gains in diffusion compensat[ing] for losses in size, and vice versa" (7, 9).
He then poses a hypothetical in which an altruist is offered a choice.* The altruist can:
" provide consistent, full nutrition and health care to 100 people, such . . . that instead of growing up malnourished they spend their 40-years long lives relatively healthy; [or]
 prevent one case of relatively mild non-fatal malaria [say, a fever that lasts a few days] for [each of] 1 billion people, without having a significant impact on the rest of their lives" (14).
Pellegrino argues that choosing the second option (the Altruistic Repugnant Conclusion) is a "necessary consequence" of the principle from above, but that "[b]ringing about very tiny, but immensely diffused, benefits instead [of] less diffused, but more substantial, benefits is seriously wrong" (15).
Based on this, he claims that "either effective altruists should accept [the Altruistic Repugnant Conclusion], thereby swallowing its repugnance, or they should give up their core tenet [of Effective Altruist Maximization]" (20-21).
You can read Pellegrino's full essay here.
A Possible Response
As Pellegrino acknowledges, "EA has often been the target of criticisms historically pressed against standard Utilitarianism[,] [and his] paper [is] no exception" (21). In light of this, one way to respond to his argument is to borrow from responses to other critiques of effective altruism that are premised on effective altruism accepting utilitarianism.
Specifically, one could argue that "[Pellegrino's] arguments appeal only to hypothetical (rather than actual) cases in which there is a supposed conflict between effective altruist recommendations and [intuition] and thus fail to show that effective altruist recommendations actually do [lead to a repugnant conclusion]."
Feel free to share other responses to Pellegrino's argument.
*Pellegrino's hypothetical is based on a similar hypothetical posed by Holden Karnofsky. In both Karnofsky's hypothetical and Pellegrino's hypothetical, there are three options. I have limited the hypothetical to two options for the sake of simplicity.