Banning of registered users happens pretty regularly. The common reason is spam. I think you are really asking about members (different from registered users) who have posting privileges disabled. That's happened on a few occasions usually for high maintenance behavior. Glade wasn't happy here. I was sorry to see him go.
"You just need to go at that shit wide open, hang on, and own it." —Camp
Harv , you have given us every latitude possible on a wide variety of subject matter . You have been more than patient and have done a very credible job of moderating this place .. ...just sayin. It ain't easy !!