[chrisnight]

Mastodon works by copying all data their users see from other servers to the server's own local PostgreSQL database.

Admins have access (through the owner or directly) to that database, which means they can already censor content if they so choose, through manipulating the database. As such, making it an explicit option is needed because it destroys any illusion that censorship cannot occur, because it can occur by the system's design, even if the option isn't present in the software.