Hi dot, thanks for posting this.
Such shunning serves to strengthen and protect the group. Not only does it remove burdensome members, but it can correct deviant behavior in such members because they will long to return to normal relationships with their former associates.
While shunning is a method that works to coerce some people, it doesn't work with me. I have NEVER been anyone who grovels after someone's attention, even from my family. If people don't want me around, I don't come around. So shunning is not a method that works all the time with all people. But I suspect it works well enough that Botchtower won't stop using it until it becomes illegal.