[riezebos]

I don't know how "at some point you end up in a position of diminishing returns" in this case is an argument against EA. In the book Doing Good Better one of the core ideas of EA is defined as investing in problems that are neglected, which prevents investing in diminishing returns. Whenever the malaria nets run into diminishing returns I am sure that GiveWell will start ranking AMF lower. If you are arguing that we should not invest in problems that have diminishing returns EA strongly agrees with you.

[TeMPOraL]

GiveWell is literally a priority queue of charities. The moment AMF starts getting diminishing returns, it'll drop down the list. If some other organization figures out an even cheaper way of saving lives, it'll overtake AMF on the list.

It's a simple and obvious system. I'd say the only two things to potentially quibble about is whether or not one likes their sorting function, and the lag time between resorting.