Karnofsky has, as far as I know, not endorsed measures of charitable effectiveness that discount the utility of potential people.

Actually, according to this transcript on page four, Holden finds that the claim that the value of creating a life is "some reasonable" ratio of the value of saving a current life is very questionable. More exactly, the transcript sad:

Holden: So there is this hypothesis that the far future is worth n lives and this causing this far future to exist is as good as saving n lives. That I meant to state as an accurate characterization of someone else's view.

Eliezer: So I was about to say that it's not my view that causing a life to exist is on equal value of saving the life.

Holden: But it's some reasonable multiplier.

Eliezer: But it's some reasonable multiplier, yes. It's not an order of magnitude worse.

Holden: Right. I'm happy to modify it that way, and still say that I think this is a very questionable hypothesis, but that I'm willing to accept it for the sake of argument for a little bit. So yeah, then my rejoinder, as like a parenthetical, which is not meant to pass any Ideological Turing Test, it’s just me saying what I think, is that this is very speculative, that it’s guessing at the number of lives we're going to have, and it's also very debatable that you should even be using the framework of applying a multiplier to lives allowed versus lives saved. So I don't know that that's the most productive discussion, it's a philosophy discussion, often philosophy discussions are not the most productive discussions in my view.