I disagree with it because like with so many issues, the JWs are black and white about it. While I think it is sensible not to rub elbows with somebody with questionable morals and practices, that doesn't mean you have to just completely ignore them. If you can't so much as acknowledge a person's existence without falling to the dark side, then you have some serious problems, and maybe the disfellowshipped person isn't to blame.
Second, it's like the JWs are kicking someone while he or she is down. I think in some cases, the JWs disfelloship someone when he or she needs help the most.