If you really didn’t want to have a category just for topics that one user, such as the admin of the forum, doesn’t want to see.
It might be a good feature to have a “topic suppress” option, or if people don’t want the extra clutter/confusion that would cause; perhaps it would be best to make sure that the relevant users of these forums are using the flagging/moderation system to reach out to their admins, etc.
maybe the “topic suppress” option would be best delivered by a plugin, so the extra clutter is a decision each community can make about whether they want that.