I do not think that a point by point response will really say the things that I want to say. I will say that you put your finger on some great points. Overall though, because you extrapolate on each Source of Authority individually I feel that you miss the fact that in all Movements, the four of these (Scripture, Tradition, Reason, Experience) play simultaneous roles, usually without the thinkers knowledge.
First a few points to clear the air. EVEN IN THE ‘CATHOLIC’ TRADITIONS THERE IS NO TRUE AGREEMENT ON ALL DOCTRINES. There are Roman Catholics who write theology and history that do not receive the Imprimatur and there are Orthodox priests who think that the Philioque is an acceptable position to hold (provided it is admitted to be a later accretion) or that women should be able to be priests. And so, as in most Protestant traditions, there is a disconnect between what the “Official Body” counts as Dogma and what the individuals within that body actually believe.
What then holds the Movements together? That is a simple answer…
A first reaction might be the Eucharist. But that is simply not true. We all partake in the Eucharist. The reason that some will not take it with others is because of Ecclesiology. Who is in “The Church” and who is out. As pointed out above, universally held doctrine is not a reality, and so it is the Episcopacy which determines unity. The unity from the Eucharist (in exclusivist Bodies) is only attainable by permission and blessing from the Body Politic. The only possible exception might be exclusivist Lutherans who really do seem concerned only with dogma. Though even there one needs permission from the Pastor before they can partake, even if one can sign the Eucharist card in good conscience.
Authority, although important, is not the unifying factor, because Authority has no place of influence outside of Ecclesiology. Diversity to a degree is tolerated within Movements because of usually unspoken rules about how much diversity can be tolerated. Only once the Movement begins to feel that some people are approaching the out-of-bounds territory does Authority begin to have a place to settle disputes and maintain unity and order.
Possible way(s) Forward:
It is funny that most of the Corpus Paulinium is devoted to Ecclesiology. While many of the words of Jesus and the Early Church are not universally applicable metaphysical laws, rather timely words of God, Paul’s struggle to ‘graft’ Gentiles into the People of God is still pertinent, still applicable with almost no anachronism. I look to Paul not because of a “biblical” authority, but because it is our earliest testimony. Earlier than the Gospels; certainly earlier than the first author to speak of the Episcopacy, Ignatius of Antioch.
Here again is the situation, this might be “New Testament 101” but it must be set up. Jesus was a Jew. He preached almost exclusively to Jews. The earliest followers were Jews. Many of them, even though Jesus had opened up a new way to relate to “Works of the Law,” still maintained their Jewish identity through the observation of Jewish ritual practices, although now shaped around Jesus whom they believe to be the Messiah. Enter, Diasporic Jews and Gentile converts, still encouraged/required to follow circumcision and kosher practices. Enter, Paul: Paul is called of God to bring in Gentiles to the People of God, around Jesus the Messiah. Paul feels that these Gentiles are brought in by Faith in Jesus the Messiah and that they should not be circumcised or required to follow Jewish rituals, but many others say otherwise. Paul fights tooth and nail and he asserts repeatedly that ALL THAT IT TAKES TO BE A MEMBER IN THE NEW PEOPLE OF GOD, THROUGH JESUS THE MESSIAH IS FAITH IN JESUS. There is nothing of Popes, Bishops, Dual Natures, Essences, Begotten Not Made, Tran/Con/Real Pres./Myst.- ation and the like.
As evidenced by the constant doctrinal correction by Paul and John especially, it is plain that often the Converts struggled to maintain proper doctrine. Even as Paul attempts to correct some false teachings that some Christians believe, he maintains that despite their confusion they are members on account of their faith.
I propose that it is a reassertion of the belief in “Justification by Faith” (as even the Romans affirm, see Hans Kung’s dissertation, or the joint Lutheran/Catholic Declaration) that should be THE DECIDING factor which determines who is part of the “One, Holy Catholic and Apostolic Church”
What of disputes then?
I say that it is the Public Discourse, focussed locally, across denominational lines, whereby doctrines are stated and tested by a simultaneous combination of the Four points of Authority. It is the accountability and submission to each other as fellow Christians which will help correct errors. A pragmatic (but not dogmatic) idea would be for us all to take on Episcopal government, but that is unlikely to happen.
In order to practice and reinforce unity by faith in Jesus Christ we should gather around the “Body and Blood” together, love each other transformationally, and practice justice in unity.