Hi Botzwana,
Alright, here's my take on disfellowshipping and the scriptures. I claim neither inspiration nor absolute correctness in my analysis :)
Considering only Jesus instructions, one does not get the impression that those who have left the faith should be shunned.
(Matthew 18:15-17) “Moreover, if your brother commits a sin, go lay bare his fault between you and him alone. If he listens to you, you have gained your brother. 16 But if he does not listen, take along with you one or two more, in order that at the mouth of two or three witnesses every matter may be established. 17 If he does not listen to them, speak to the congregation. If he does not listen even to the congregation, let him be to you just as a man of the nations and as a tax collector.
(Matthew 9:9-13) Next, while passing along from there, Jesus caught sight of a man named Matthew seated at the tax office, and he said to him: “Be my follower.” Thereupon he did rise up and follow him. 10 Later, while he was reclining at the table in the house, look! many tax collectors and sinners came and began reclining with Jesus and his disciples. 11 But on seeing this the Pharisees began to say to his disciples: “Why is it that YOUR teacher eats with tax collectors and sinners?” 12 Hearing [them], he said: “Persons in health do not need a physician, but the ailing do. 13 Go, then, and learn what this means, ‘I want mercy, and not sacrifice.’ For I came to call, not righteous people, but sinners.”
Jesus said "let him be to you just as a man of the nations". The watchtower 99 10/15 p17-20 has a discussion of this.scripture. Regarding it, the article says:
w99 10/15 p19 par 6 "Jesus' disciples hearing those words knew that their countrymen would not socialize with Gentiles. And they definitely avoided tax collectors, men who were born Jewish but who turned into misusers of the people."
I don't really buy that explanation because Jesus wanted his followers to follow his example, not the Jewish customs of the time. Matthew 18 and Matthew 9 make it clear that Jesus ate with tax collectors and talked to Gentiles on occasions.
Now we have the apostles who started to set up guidelines as problems rose in the congregation. Notice who is addressed in this scripture:
(1 Corinthians 5:9-13) In my letter I wrote YOU to quit mixing in company with fornicators, 10 not [meaning] entirely with the fornicators of this world or the greedy persons and extortioners or idolaters. Otherwise, YOU would actually have to get out of the world. 11 But now I am writing YOU to quit mixing in company with anyone called a brother that is a fornicator or a greedy person or an idolater or a reviler or a drunkard or an extortioner, not even eating with such a man. 12 For what do I have to do with judging those outside? Do YOU not judge those inside, 13 while God judges those outside? “Remove the wicked [man] from among yourselves.”
Here it seems clear to me that one would not eat with a "anyone called a brother" who is practicing serious sin. Once they are removed from the congregation, the judging is done. God judges those on the outside. The scripture does not say to continue judging them once they have been removed from the congregation?
A second category to be avoided is the antichrist:
(2 John 7-11) For many deceivers have gone forth into the world, persons not confessing Jesus Christ as coming in the flesh. This is the deceiver and the antichrist. 8 Look out for yourselves, that YOU do not lose the things we have worked to produce, but that YOU may obtain a full reward. 9 Everyone that pushes ahead and does not remain in the teaching of the Christ does not have God. He that does remain in this teaching is the one that has both the Father and the Son. 10 If anyone comes to YOU and does not bring this teaching, never receive him into YOUR homes or say a greeting to him. 11 For he that says a greeting to him is a sharer in his wicked works.
(1 John 2:22) Who is the liar if it is not the one that denies that Jesus is the Christ? This is the antichrist, the one that denies the Father and the Son.
If we take the simple definitions of that antichrist as those who do not confess Jesus as coming in the flesh and those who deny the Father and the Son, that applies to pretty much all atheists and non-christians (the JWs would also apply it to "Christendom" since they deny the "truth" about the father). To me (in JW land), I think this means that we should treat the antichrist the same as a "worldly" person.
In what sense do we not invite them into our home or say a greeting to them? I found an amusing article regarding this with a Christian asking if, in light of 1 John 10, it is okay to invite JWs or Mormons into their home. (http://www.ronrhodes.org/q2john10.html). The basic thrust is that at the time, Christians met in private homes for worship. Thus it would not be right to allow the antichrist's in to worship/teach together. This is similar to how we JWs would not worship with people of other religions either. This whole argument assumes that by receiving them into your homes or saying a greeting to them actually means "in worship". I'm not entirely convinced that it does, though.
In summary, people have a tendency to try and spin the scriptures to match the teaching they favor most. Both sides can have good points. I think the Bible has generous room for interpretation on this matter, and it is better to err on the side of Jesus' love rather than Pharisee's rules. Forcing people to completely reject their family and friends and calling it "love" just seems to far from the love that Jesus taught.
Feel free to challenge any of my points. I'm still forming my thoughts on this (ask me a year ago and I would have wholeheartedly agreed that disfellowshipping as practiced by JWs is scriptural. I felt that between that and the preaching work it was a sign of true Christianity).
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On a completely different (non-scriptural) level, I think that any form of mandatory shunning of opposing people/information is a form of manipulation used by an organization, whether religious or political, in order to keep control of their subjects. If you've never read the novel "1984", I'd highly recommend it.