There are a lot of tanky posts coming from lemmy.ml. Their whole purpose seems to be to troll and spread their bullshit far and wide. They are nearly as bad as the alt-right. They argue in bad faith and celebrate authoritarian oppression. The beehaw mods might want to consider defederating.
I wouldn’t recommend this in general. The instances you block still influence things via comments and votes and posts in other communities.
Sorry I just find this kinda funny, aren’t a lot of anarchists saying that “rival fiefdom” is exactly how society should function? But I guess anarchy is a very broad term so I might be talking about a different anarchy than you are talking about.
‘Fiefdom’ is a domain of a feudal lord, which would not be anarchist, by any definition.
If you simply mean that different groups with different sets of rules and outlooks exist, then sure, but that is abstract enough not to really be specific to the Fediverse; most other social media platforms also have some form of private groups too.