As I personally have ostracized toxic people out of my life, I sincerely do believe that we should uphold the right to shun.
There is no such right, it's more a right not to have the government force association on you.
However, religions/sects, like the Jehovah's Witnesses, take it to another level. They organize and enforce it, in the deliberate desire to torment the victim.
It's part of their belief system, like others. There are other situations where people who don't abide by a groups rules are expelled (school) or rejected (fired from work) but only the devout tend to abide by it over personal connection.
In Canada, organized shunning is considered "bullying" and within the workplace, companies can be held responsible for tolerating such behaviour. Why should this not be extended to religions who enforce the shunning of young adults who leave their religion?
Can you point us to the law / legal definition where this is defined?
It is one thing to preach about it and it is entirely another to severe against those who choose to ignore the counsel. Religions should clearly inform their members that such matter is left to their conscience and is their personal decision to make.
Which is exactly what they do. They make all these things into a 'personal choice' both to cover themselves and to convince people to follow the rules.
"A good Christian wouldn't want to do XYZ" <- their belief about desired behavior
"You want to be a good Christian don't you?" <- the suggestion that you should follow the belief
... and we're back to the fundamental issue: people have a choice to a) believe this and b) stick to their beliefs
The fact that many don't continue to believe or don't stick to them even if they do shows it's a personal choice whether to do so. There's simply no escaping that.