If I'm outside some ideological category looking in, such as in this case, communism or Christianity, and I see two groups within that category arguing over who is the truer adherent to their ideological category, that's an internal dispute that, when appealed to as the basis for claims that one side or the other of that in-group don't truly belong there, simply is not a convincing argument for why I, as an outsider, should consider that portion of that category "Not really part of it" or whatever.