S[h]unning violates the law of coercion.
No it doesn't. In Criminal Law (at least in the US) for duress/coercion to be considered a "crime", it must meet certain requirements, the first of which is "The threat must be of serious bodily harm or death."
The question is if you didn't have this rule and your own fear of being shunned......... would you still maintain some level of contact with the person who has left the JW construct?
This happens all the time outside of religion. A circle of friends may end up shunning a member of that circle because of some perceived wrong. Other members of that circle may fear associating with that shunned member because they themselves don't want to be ostracized by the others in the group.
Is this toxic behavior? Clearly. Should this be considered a "criminal offense" in a free society? Of course not. I reserve the right to shun people that behave this way.