In response to a very kind email that I received, I want to clarify something I wrote previously.
Yes, everyone sins and every sin is an act of rebellion against HKBH's sovereignty. But there is a vast difference between one who slips and falls on the proper derech and gets up again and continues on in the path towards Hashem and one who turns himself around and flees in the opposite direction and essentially removes himself from his people. However, even such a person, as a fellow Jew, I would extend a greeting to him. But there are some who go so far in their rebellion that they become an outright spiritual danger to the Jewish people and it is to these that I then go so far as not to give a greeting. With someone I know from my own experience is actually a rodef, bringing about physical or spiritual harm to other Jews, I can not say "shalom," because there is no shalom between us. And this person can only fix this situation by abandoning his rebellion. Until he does, he needs to be put "outside the camp" for the protection of others who could come under his influence or suffer at his hands.
In my position, I can think of at five people of my acqaintance that this applies to and three of them are rabbis teaching heresy. The other two engage openly and favorably with missionaries and bring them together with Jews. Obviously, then, I'm talking about very extreme cases. And those who are equipped to deal with kiruv situations have their own set of guidelines, I'm sure.
I thank the writer of the email for giving me the opportunity to clear that up. Often when we speak or write, we know what we have in mind, but it doesn't always come across when communicated.
Looking forward to the day when all Jews can enjoy complete achdut,