I suppose that if a JW sincerely believes that:
- Apostates will be killed in Armegeddon and
- Shunning an apostate will motivate them to return to the fold
Then shunning could be a (misguided) display of love or a form of "tough love". However, I often got the impression as a JW that it was really more about protecting one's own reputation by not consorting with unclean people like apostates and nonbelievers. Apostasy is analogous to a disease and so the wisest thing to do is to enforce a quarantine until the diseased person is cured.