This is surfacing a fundamental division between mindsets in federation: the people who say don't worry about which instance you're on are bought into the promise that federation can "just work" like email. But the reality is that if you care about moderation at all (like, even to the extent of being for or against having any of it) then sooner or later you're going to have to make harder decisions about instances.
It's pretty normal for long-term fediverse users to change instances several times over the course of however long this stuff has been around. It's unclear to me whether any existing Lemmy instances would be a good fit for me in the long term TBH and I would expect that to be true for some time, as so many instances are still figuring things out internally.
Defederation decisions like beehaw made are extremely normal and rational. With their level of moderation staffing and for their user base, they determined it was unsustainable to remain federated with instances that were generating more moderation workload. If it wasn't them today it would be another instance tomorrow; this will keep happening.
Also, I see a lot of folks saying this is lazy for beehaw, but it's important to understand that from their perspective, this problem wouldn't arise if moderators here were keeping a cleaner house and preventing bad actors from using the platform. (Not saying either take is entirely correct.)
In a sense, moderation best practices on the fediverse are inimically hostile to scaling the fediverse up to new users. (And if you ask folks with smaller but prosperous instances that have healthy internal vibes, they'll probably tell you this is good.)
This is much more fraught on Lemmy than it is on Mastodon, because you're building communities hosted on a particular instance and there's not currently a way to move the community. So, if I were to start a community here and then finally decide a year from now that this place is too big a defederation target to stay on, what do I do?
Similarly, to avoid endless duplication of communities, folks have been encouraged to participate with existing communities instead of starting a new one on their own instance everytime. But anyone here who has gotten involved with communities on Beehaw will now no longer be able to do so unless they move to a different instance. (Which may be hard, as open instances that are easy to join are the ones that are harder for small instances to handle, which is what caused this in the first place.)
Some of those folks are going to create their own alternative communities on their servers, which to any third-party servers not in the loop on the defederation drama will be potentially confusing. This has the potential to create a cultural tend toward polarization of community norms between everything goes and what we see on Mastodon as content warning policing, but of which are, to me, undesirable.
The best case scenario is that the majority of large communities end up being hosted on instances that have sufficiently rigorous moderation standards and sufficiently robust moderation staff to not impose an unsustainable workload on smaller instances. Then as long as everyone who's not a nazi federates with those instances, things should go smoothly...ish. But that's hard both because "sufficiently rigorous" is different for everyone and because moderation labor doesn't grow on trees.