I thought independence of the organization was evil.
It's just the opposite as far as the borg's lawyers are concerned.
In the event of a lawsuit (such as the Conti case), the GB wants the local JWs to be seen as independent volunteers rather than as agents of the organization.
Allowing publishers to write letters using the Society's address would be seen as evidence that they are acting as agents of the organization in what they do.
Can't have that!
The whole thing is ironic and hypocritical, given the vast control the GB exercises over Witnesses' lives: "Do everything we tell you to do the way we tell you to do it, but if you get into trouble doing it, you're on your own because you're just an independent volunteer."