How and why would any government ban the ability of this one group to follow this one behavior vs other groups and other beliefs?
People can be free to make their own choices and treat people how they choose to do so. But when the groups leadership puts in writing things such as, "Don't look for excuses to talk to your family, even by email", the government can put a stop to that. That order members to shun family be not allowed and each to decide on their own.
Tell us how it would be enforced - would a government official accompany you to someone's house and command them to talk to you?
The law could hold the GB and printers responsible for what they print. They could get things from jail time or even just loosing charity and non taxable status. If a charity is teaching hate and breaking up families, why should they be exempt from taxes? I bet that the $ would make the GB change their tone real quick!
What is the point of demanding something if it would be utterly and absolutely impossible to legislate? Have you read the articles on the florist who refused to give gay couples flowers for their weddings. Their beliefs weren't honored on them not believing in gay marriage. The law didn't tell them to just go elsewhere as many others would be willing to sell flowers. So when a religions leaders are instructing to do something harmful to children, families, etc, why would that be 'impossible' to legislate? It's far from impossible.
We have to be pragmatic - how would a court decide what was hurting vs "protecting the congregation" as the WTS would claim?
The court could make and force them to uphold what they claim and try to sell to the public their policies as. Since they try to make their policy under FAQ appear to be that family ties remain no matter what, only no spiritual talk, the court could force them to uphold it that way. They try to recruit members claiming worst case if anybody in the family leaves is no more spiritual talk but still family, that they abide by that. Or put a big disclosure on their study material like cigarette companies, etc, are required to do, "By joining Jehovah's Witnesses, if anybody in the family later on leaves, those who remain are required to shun them for life should they never return. It doesn't matter whether they break laws in the bible or not, we believe those who don't obey the Governing Body must be shunned." They can force a real disclosure of their true beliefs upfront instead of beating around the bush and trying to whitewash it.