Oh I would agree that many if not most do it because they think it is truly the right thing to do. What I do not understand is that so few actually try to find out if it is truly what God wants. So here we must decide if it victim or willing victim.
Are there less destructive ways to show disapproval for ones choices in life? For example, I know a Christian couple that were very disappointed when their son moved in with his girlfriend. They consider this living in sin. Now, if they were jw I would imagine they would be required to shun this son (after the jc when elders found out). But instead the son and girlfriend are allowed at the parents home anytime. The parents however will not be 'entertained' at the son and gf house. I am not trying to open up a discussion on living in 'sin' here. Just trying to point out that the parents are able to show the disappointment and religious beliefs to their adult son and mantain a relationship with both the son and most likely their future daughter in law. The parents in this case wish maintain a relationship to further be an influence in the lives of these two young people. How could they show anything if they no longer spoke to them? How could they be a 'light to the world' if they hid away their love for their child? The gf sees the relationship between the husband and wife and is quite taken by it. She sees love, friendship, and the continuous love for their child. In doing so, the bf & gf are thinking marriage and what that really all entails. None of this would be possible if the parents had shunned the son. The son and gf are talking about things most young people don't even think of before marriage, children, faith, money, resolving disputes, even holidays and family traditions.
It's just all so maddening. The pain I see due to shunning and of course all the rest. We hit our collective heads against the wall and ask why? Always hoping to find the magic bullet that will open their eyes, and it doesn't exist. So we plug along always hoping.