If I sent several RPs about my character running over plans in his head about how he was going to kill the duke, would you expect the entire realm to just ignore it? If I went to try the hit and saw that for the next several days there were people out patrolling the streets to make it harder, should I start screaming "Powergamer!" because there are police patrols around when there really isn't any valid reason? (Or at lest one that I know of.)
Without question, yes.
Or how about if I RPd my character thinking about the coming rebellion, and listing the names of my conspirators, and how we're going to get the army sent away so the plan works easier. Is the entire realm supposed to just go along with the orders, knowing full well that as soon as they get four regions away for the capitol, that the entire home guard army is going to rebel?
Ideally. I doubt that everyone would, given that a lot of people are probably going to want to save their power in the realm by any means even if it means violating OOC/IC separation, but ideally, yeah, and I bet it would be pretty fun for everyone involved. But I doubt it will happen.
Can you see how this kind of thing is entirely unfair to the rest of the players of the game, making them try to remember to separate all this information that the player knows but not the character? You're forcing everyone in the realm to just have their character blindly go along with this, knowing that their characters are walking into a trap.
That's part of roleplaying, separating stuff you know from what your character knows. I don't see how it's at all unfair if BM is a roleplaying game.
And then let's not forget that you /always/ have the opportunity that someone just innocently slips and uses the info IC because they forgot that the information was sent as private thoughts. Then how do you resolve those kinds of things? Especially if the slip happens when the "thinker" character doesn't see that the information is being passed. Like it gets sent to a foreign ruler. And then that foreign ruler thinks that the info is perfectly valid IC info and spreads it around.
Slips happen. One hopes that people can be forgiving of accidents, just as one hopes that people would not deliberately misuse OOC info. Experience shows that neither of these are always the case, of course, but that doesn't mean we shouldn't hold them up as ideals.