One factor at play here is that the “best possible” thing to do isn’t just incredibly difficult to figure out, as you rightly say, but also an extremely (indeed impossibly) high standard. It’s human nature to have many different motivations, drives and values (in a broad, loose sense of ‘values’) besides purely altruistic ones. Few if any EAs I know do, and I certainly don’t judge them for this or want them to feel bad about it—apart from anything else, that wouldn’t help anyone :)
I expect pretending otherwise would be to place counter-productive pressure on people. Of course when there are valuable actions that people can viably take it can be good to nudge them into them, but there’s a balance to strike here, and it does no good to push people too far or too hard. But as you say there’s definitely a way to do this that’s nice, gentle and focuses on concrete improvements—after all, we’re all working together towards shared ends. The attitude that common sense practice and morality would recommend taking in this plausibly embodies some wisdom, informed by an understanding of human nature built up over the centuries.
Great post Jess!
On the birthday fundraiser, we’ve just made a form where you can indicate that you might be interested in having one next time you age: http://www.charityscience.com/birthday-fundraisers.html . People are finding their friends really responsive, so it’s a great, natural opportunity to direct money to some fantastic charities!