I don't see how this would be abuse, but destroying the whole realm wouldn't...
"I hate the King of Kepler. I want him dead, gone, erased from history, his name forgotten. When I'm done with him, there won't be a Kepler left." is a perfectly legitimate, IC sentiment.
"I hate the King of Kepler. I'll ask the Count of Kepler Fields to swear allegiance to Evilstan, evince him from his manor, then come back to Kepler" is not something a medieval noble would do. It's meta-gaming.
