What about a peer review system for messages reeking of thoughts of equality? Messages would be reported and reviewed much like the vulgarity reviews, but if the messages is deemed offensive, there would be far steeper penalties. Somewhere between a quarter and half the offender's H/P would drive the point home nicely, I think. Perhaps make the messages 'anonymous' when sent for review, as in leave out the name of the noble writing it, so there is no chance of nobles taking a chance at screwing over someone they don't like when asked to review their messages.
