BP,
The problem is if the 'banished' person knows your stores, defenses, methods, etc, then they are a huge liability. They will go out, find the first big armed group they can find, and tell them everything about your group and what they can take from you. They will use information on your group to 'pay' for admission into the other group.
Banishment could mean the death penalty for them, or for you. I don't know how you avoid that problem.
The problem is if the 'banished' person knows your stores, defenses, methods, etc, then they are a huge liability. They will go out, find the first big armed group they can find, and tell them everything about your group and what they can take from you. They will use information on your group to 'pay' for admission into the other group.
Banishment could mean the death penalty for them, or for you. I don't know how you avoid that problem.