"A stronger community for the effective altruist movement should better encourage existing EAs to contribute more and better attract new people to consider becoming EA. By building the EA Community, we hope to indirectly improve recruitment and retention in the effective altruist movement, which in turn indirectly results in more total altruistic effort, in turn resulting in more reduced suffering and increased happiness."

I'm going to predict that .impact struggles to meet this objective.

I think you're taking a naive view of how movement building works.

I think you need to see the distinction between retaining and recruiting members as analogous to the tension between a core and casual fan base. In order to recruit new EAs, your pitch will almost definitely have to downplay certain areas that many core EAs spend lots of time thinking about. That way, you'll bring in a lot of new people that, for example, buy the argument that you should donate to the charity that provides the most bang for your buck and yet still, for example, have zero interest in AI or animals. If you refuse to alienate core EA member values in order to get more casual EAs (e.g. people that donate to GiveWell's top charities and give a bit more than average) then, well, that's admirable, I guess, but you're movement building won't go anywhere. There's a reason why for-profit organizations do this - it actually works.

The amount of people that share most EA values is going to remain low for a very long time. Increasing that number wouldn't involve "recruitment" as much as it would involve full-on conversion. As long as your goal is to increase that number, you're going to see very low recruitment rates. Most people aren't on the market shopping for new worldviews - but individual new beliefs or values, maybe. And if you won't agree with a worldview, you aren't going to join the community just because it's active.

If you want more "total altruistic effort," go convince people to show more altruistic effort. Trying to movement build a group as complex and alienating as EA by strengthening its internal ties will dissuade most outsiders from wanting to join you. Pre-existing communities can be scary things to self-identify with.

You know how some parents make their kids try cigarettes at a young age so that they'll hate it and then not want to smoke when they're older? Well, a website like Brian Tomasik's is like that for most potential EAs. Way too much, too soon.