After talking with LilWolf on IRC:
It is true that Tom, the Titans, the devs, the Magistrates, etc cannot realistically police the (ab)use of such information.
However, the current guidance on the Wiki—and Tom's official position—is, indeed, actively chilling potentially positive roleplay within the game.
If it is desired that this be something that the players police for themselves, then why not say this? Rather than just a blunt statement that OOC information being used IC cannot be punished, why not say something like the following:
"Use of OOC information IC, or use of information from people's roleplays that you would not reasonably be able to obtain access to in-character, is strongly frowned upon, and it is expected that the players will police this and deal harshly in-character with those who show up with knowledge they could not have obtained save through dark magics."
This could go a long way toward changing the atmosphere and attitude toward such actions. If it was considered unacceptable by the majority of players to use such information nefariously (at least openly), we might very well see a lot more interesting RP—and I think a lot of us would enjoy that.