That is their choice, instead of seeking game mechanics to punish them, use the existing tools to rally the realm against them and prevent them from doing so. If you can't convince the realm to act, then its simply not a problem the realm cares about enough.
Why is it seen as a punishment? You want people to punish them for doing that, not me.
Honestly, the more this goes, the more I have a simple solution: abolish academies altogether. Training is not fun. Having others spend huge resources on training is not fun. Infiltrators aren't even as meaningful as they used to be. Gameplay-wise, there's no reason to have academies around. People who want to train should pressure their leaders to hold more tournaments.
