[Tollund]

If you can't take his castle without gems, then don't take it. Preach him out or jus leave a sigle unit there and move on to his other provinces. What you are asking for is for your enemies to give up as soon as they attack you. Burning 10-25 death gems to get your opponent to spend his own gems seems like a perfectly reasonable exchange to me. Next you'll be complaining that people shouldn't be allowed to play kingmaker, to throw the game, to trade gems or items or to donate their gems to the enemies of the person who just killed them.