To put this a different way, it functions like a block. People want to block the entirety of Threads because we don’t trust Threads.

@Roflmasterbigpimp Every account on the Fediverse is hosted by an instance on a server, the admin of each instance can choose to defederate from any other instance if they don’t want content or users from that instance to be intractable with their users or visa versa. This is often done due to differences in “terms of service”, for things like hate speech, CP, or just political differences. Some instances will have zero NSFW policies, some will have defederated communities/magazines for content private to that instance (lemmynsfw does thus for example).