This has nothing to do with individuals who shun people. Nothing. It has to do with religions, groups and others that practice Mandated Shunning - yes, I realise this now. I didn't read thru your post properly.
Nevertheless, even if governments try to legislate only mandatory shunning, it is still going to be difficult to put it in law and choose the right wording.
If individual shunning is ok, why can't groups have rules on mandatory shunning (written or unwritten) as part of their beliefs?
It also seems to be a poor choice of time for the authorities to run this legislation thru their respective parliaments. And it seems to be a poor choice of time for law enforcement to spend time on investigations into organisations practicing mandatory shunning. Why? - well because their are enough serious crimes for the authorities to legislate against and tackle. The authorities should devote their energies to these first.
I live in the UK. Over here, there have been cases of people reporting crimes such as theft to the police, with the police saying that there is nothing they can do. It would be a bit weird that, while the police said there's nothing they can do about theft, they then spend time and resources questioning cult leaders under oath about whether mandatory shunning is part of their rules. And then taking them to court if the cult leaders refuse to comply (!).
Let's say that this goes ahead and mandatory shunning is made illegal, and high-control groups such as the JWs comply. So now shunning is a conscience matter, i.e. it's now individual shunning. That's what the JWs would do. Have nothing currently in print about it, but the higher-ups would have discreet chats with rank and file as necessary. How could authorities stop this? Because it would happen. Shunning would be similar to how the org goes about practicing theocratic warfare.
There is another way to deal with mandatory shunning, besides falling back on legislation.
How about this: government threatens to take away Watchtower's charity status if they continue with the mandatory shunning.
Don't get me wrong, shunning in general and mandatory shunning cause lots of problems.