a) If you look at it scripturally, you would find that Jesus was cautioning the world against JWs (who keep on changing the time-table of Jesus’ coming/end of the world) when he said:
“So if anyone tells you, ‘There he is, out in the wilderness,’ do not go out; or, ‘Here he is, in the inner rooms,’ do not believe it. For as lightning that comes from the east is visible even in the west, so will be the coming of the Son of Man.” (Mathew 24:26, 27)
These verses and his previous caution (in Mathew 7:21-23) clearly prove that no organization is appointed to announce to the world the presence/coming of Jesus.
b) If you look at them from the level of common sense, you would agree that we are all human beings first (from humus, Latin, soil/physical elements + being or conscious/immaterial entity) which means we are all children of God--an ultimate truth, glory of which cannot be shaken by too weak reasoning such as 'if one does not share our belief system, we should not greet him.' Yet JWs practice shunning as a weapon which makes them inhuman.