Simon,
It has been theorized that tension is essential to survival and growth of a new religious movement. (Stark and Iannaccone, 1997 Journal Cont Rel) According to this theory the trick is having and asserting a relatively unique strictness that strikes a balance between to much and to little tension.
When I look at Watchtower's organized communal shunning policy I see a religious movement using tension as a method and means of growth. This presents as a dial that can be increased of decreased in multiple ways, but in each case in a way that projects overall growth.
Just to dial in what I think is a primary personal accountability problem for JWs, I think your statement "some JWs are unloving and unchristian because they choose to shun their loved ones" is better to read JWs are unloving and unchristian because they choose to shun their loved ones based without knowing precisely what the individual is supposedly guilty of doing. It is, after all, Watchtower policy for elders not to disclose details of a judicial case and loyal JWs are not supposed to communicate with a disfellowshipped individual about why they were disfellowshipped (which supposedly falls under the broad subject of "spiritual").
From a purely biblical perspective (something JWs are told is paramount!) the model is to inform the church membership what precisely the individual is guilty of, whether that be having a sexual relationship with their father's wife (see 1 Cor.) or apostasy (see 2 Tim.) Watchtower defies this biblical model suggesting it is hostage to contemporary legalities. Yet contemporary legalities do not seem to interfere with other Watchtower policies, such as the one known as Theocratic War Strategy. When Watchtower wants to assert a policy it does so whether it complies with black-letter law or not.
___
