it's well-known that most religions DO ex-communicate members as a means of punishment (behavior modification),
There are significant differences between WT disfellowshipping and excommunication as practiced by most Christian sects:
(1) WT makes a public display of doing so, rather than doing so privately.
(2) WT insists that all in the congregation ignore and shun the person in a mass display of humilitation, rather than limiting the punishment to exclusion from the community worship.
(3) WT requires a long period of public repentance and humiliation for the person to be reunited with the congregation, rather than a quick (often immediate) reconciliation upon expressing repentance.
(4) Because of the public action (1), encouragement for person-to-person punishment (2), and the continued sanctions even after repentance (3), the effects may linger indefinitely. This is not the closure promised by "Neither do I condemn thee: go, and sin no more" (John 8:11)