I disagree. It'll discourage leaders to use the public channels to discuss and plan as random newbies might get their messages and share it with their new realm.
At some point you have to consider, do I want to try what I can to keep things secret, or just share it with the realm so that everyone feels involved? Keeping things too much behind closed doors also frustrates a decent amount of nobles, people want to be involved, rather then just order following nobles. Ofcourse, you can't share everything, but most, you can.
