I think the claim, which I do not necessarily support, would be this: Many people give to multiple orgs as a way of selfishly benefiting themselves (by looking good and affiliating with many good causes), whereas a “good” EAer might spread their donation to multiple orgs as a way to (a) persuade the rest of the world to accomplish more good or (b) coordinate better with other EAs, a la the argument you link with Julia. (Whether or not there’s a morally important distinction between the laymen and the EAer as things actually take place in the real world is a bit dubious. EA arguments might just be a way to show off how well you can abstractly justify your actions.)
I think the claim, which I do not necessarily support, would be this: Many people give to multiple orgs as a way of selfishly benefiting themselves (by looking good and affiliating with many good causes), whereas a “good” EAer might spread their donation to multiple orgs as a way to (a) persuade the rest of the world to accomplish more good or (b) coordinate better with other EAs, a la the argument you link with Julia. (Whether or not there’s a morally important distinction between the laymen and the EAer as things actually take place in the real world is a bit dubious. EA arguments might just be a way to show off how well you can abstractly justify your actions.)