Jeff Benner@gruber for some marginalized people, a draw of Mastodon is the ability to create communities with moderation that ensures safety. What Bluesky or Meta joining ActivityPub means to them is the likely collapse of that safety, as they offer a large volume of new users on servers where their track record for moderating hate and violence is poor. It makes sense if those communities want to commit to a defederate and see approach. Tech journalists will be covering their trust and safety issues.
@gruber I take your point that open means federation of instances, but I think open also means defederating when abuse or the likelihood of abuse warrants it. Open is also freedom of choice. Users that want to engage with Meta and Bluesky can move to more federated instances.