Yechi, saying that the rebbe instructed them to do so only is a justification if you accept the authority or legitimacy of the rebbe. I accept neither. To me, he made a mistake in telling people to go into other communities which were doing fine on their own and try to convert them into chabad chasidim. It’s arrogant, chutzpah, and is breaching a boundary of mutual respect that the rest of klal yisroel has for one another.
Even groups that do not get along – we don’t see MO people going into yeshivos, or yeshivish people going into MO shuls to spread their ideas.