Ok this is all fair. I think, however, that a big fraction of the historical impact is due to on-going activity, of the kind that could continue, rather than being all due to the ‘set up’ generating the stream. And that would mean the historical ratio is a reasonable guide to the future.
This can be hard to see from the outside, but if you look at where new pledgers are coming from, it’s often new press coverage or student group activity. Many also only take the pledge after being nudged by someone in person, even if they had heard about GWWC some time before, so there’s an important role just talking to lots of people about the pledge. These kinds of activities can be scaled much further.
I replied in the other thread: http://effective-altruism.com/ea/hz/please_support_giving_what_we_can_this_spring/
That reply:
Continues at http://effective-altruism.com/ea/hz/please_support_giving_what_we_can_this_spring/3vw