Playing devils advocate here....
What relationship does shunning have with tax? You can try and promote shunning as a human rights issue but you can't force someone to talk to another person. There are clear rules around how a disfellowshipped person should be treated and it's made clear in the questions reviewed before baptism. You join the club knowing the terms of membership.
Of course it can be argued that shunning produces a framework of mental coercion to ensure compliance but equally no one is physically prevented from leaving. No one physically forces you to go to the meetings. Jehovah's Witnesses are by no means the only religious organisation that have shunning. There are loads of other organisations that have charitable status with far more extreme views. If you tried to tax the JWs for having some practices that are not the most liberal and inclusive in the world then it's going to have massive implications.
I think it's a hard enough job to try and question the charitable status of Jehovah's Witnesses on high profile questions like charitable works and child abuse policies. Imagine the field day WT lawyers would have fighting restrictions based on shunning.
Punk is absolutely right - until not shunning brings in more money that shunning then it's use as a control tool fair outweighs anything else.