Ultimately, an overwhelming majority of Christendom resides within Liturgically based, Hierarchal Churches.
Major Traditional Branches of Christianity
(mid-1995; source: Encyclopedia Britannica)
Branch Number of Adherents
Catholic 968,000,000
Protestant 395,867,000
Other Christians 275,583,000
Orthodox 217,948,000
Anglicans 70,530,000
Source
Accordingly - and without even touching upon the clear Scriptural dictates we accept for both - pragmatically, this same vast majority is far more rightly concerned with healing past schismatic rifts which serve to divide us on otherwise common grounds than in arbitrarily subscribing to the individualistic and anti Liturgical, anti Hierarchal, doctrines advocated by "Gospel Union" - or by anyone else plainly well beyond the Christian mainstream we so obviously represent.
However, while a practicing Catholic, I regularly work in common cause with fundamentalist Protestants on "the Christian Right" on a host of societal - "family values" - issues, none of us compromises or abandons any personally held theological principles to do so.
In the final anlaysis, what Christian can ever aspire to be - or need be - anything more than "the thief on the right"?
I don't doubt that hierarchical Churchianity is the mainstream, and I don't doubt that there are faithful believers with varying levels of maturity and faith scattered among all (or most) of the denominations and factions. But that doesn't make the denominations "the kingdom" or a "piece" of the kingdom. The kingdom of Christ resides in each of us who are in Him, and doesn't have an address listing in the phone book.
Individuals might mistakenly submit to faulty systems of authority and clergy who are not authoritative in the eyes of God, but that doesn't mean they are lost. We are responsible for what we understand, and when people come to understand that professional clergy bear no God-ordained authority, they will figure out what to do.