participate the effort to create an alternative to Reddit people leave Reddit to join the alternative be unable to handle the influx of people trying to use the alternative to a website with millions of users

Their reasons are much more selfish than that. They insist on only having 4 moderators while never scaling up, and they don't like how federation allows users from other instances to post on their instance because it disrupts their rigid ideal community vibe. According to their suggestions on "improving moderation tooling", the ideal federation setup is that their users can post on other instances, but other instances' users can't post on theirs, so they can save time on moderation work. The moderation work of other instance admins for their users doesn't matter, clearly.

Isn't this like... the whole point of the Federated Universe? The mods do Beehaw want their server to be a "safe space". They're perfectly within their rights to restrict who can post in their own community. But you, the user, are not in any way beholden to their whims, and can make an account on any other Lemmy instance, or create your own and make it as restricted or unrestricted as you please.

It seems logical to me that the creators of a safe space for marginalized communities would restrict their community from the internet at large because people on the Internet feel emboldened by anonymity to attack others.

Yes, the point of the Fediverse is that everyone is free to associate with groups they choose. There is nothing wrong with creating instances that are very isolated. What Beehaw wants with the "improving moderation tooling", however, is a safe space where the network is restricted from them, but they still have full access to the rest of the network. That suggestion is what I was calling selfish, because this way their users would be parasiting off the content and moderation of other instances while giving nothing back.