You raise some good points, Simon.
First, one must discern the distinction between Christian dis-fellowshipping (1 Cor. 5:11) and shunning (2 John 9-11). To understand what Christian dis-fellowshipping is, one must understand what Christian fellowshipping is: A sharing of spiritual association. To discontinue spiritual association with a "brother" who is an unrepentant evildoer (defined at 1 Cor. 5:11) does not require refusing to greet such ones in normal social situations. Paul said to "keep this one marked, stop associating with him...yet do not be considering him as an enemy, but continue admonishing him as a brother." The only persons Christians are warned about greeting are former Christians who have rejected "the teaching of the Christ." (2 John 9-11)
I feel that dis-fellowshipping and/or shunning should be a strictly personal decision, and should not be mandated by any organization.
Some JWs feel it is proper to shun inactive family members they encounter at family funerals.