If a need- to-be-disfellowshipped would be really so devian and dangerous for the congregation to deserve to be shunned....why the elders then follow the disfellowed-subject, trace the lost sheep, go behind it, speak with it and invite it to return to the congregation with words like "we really miss you"?
In most cases the disfellowshipped are not harrassers, professional whores and professional malesluts but only week and doubters of some doctrines, inexperienced, to much inobiedient, immature ?.