Without reading everyone else's comments, I think it FEAR is what makes people OK with shunning. Fear of what others will think. Fear of displeasing [insert authority figure here (ie: Parents, Elders, Congregation, Org Leaders, Jesus, Jehovah, Angels, etc)]. Fear of reprecussions. Fear of having to take respnsibility for their own thoughts and actions. Fear that if they take that first step in talking to someone who has deliberately chosen a different philosophical path that they will be unable to maintain their own integrity.
Fear is a strong motivator in many.
-Aude Sapere (meaning: Dare to Know; Dare to Think for Yourself)