But I think that the Mormons make a reasonable point when they say "Our church doctrines were arrived at via councils composed of men, and as a matter of fact, so were yours."
One could be a Nestorian, or a Socinian, or an Arian, and have an equal right to claim the title of "Christian". It's just that those beliefs failed to win the approval of the Roman and Catholic power structures and therefore have gone down in history as "heresies".