Francis Berger initiated the debate - and Orthosphere writers JM Smith and Kristor have thus-far responded.
My attempt here is to try and summarize briefly what I believe the debate to about About.
In other words - what do I regard as the ultimate question behind the rather complex arguments on both sides.
I think the ultimate question is something like this:
Is The Christian Church (in some sense of The Church) in-charge-of human salvation - or is salvation primarily a matter for each individual.
I think that all sides agree that individuals may err in their discernments and choices, and that such errors and choices may lead to that individual being damned.
The question is whether The Church (which in practice means My Church, in the way I conceptualize it) can err in an ultimate sense - such that The Church's errors will lead devout and obedient members to damnation.
My understanding of adherents of the Altar-Civilization Model, is that they are rooted in the conviction that (in an ultimate sense) The Church cannot err on the matter of salvation - whereas individuals can and do err; and therefore The Church will ultimately know better than any individual; and therefore the path to salvation is necessarily via obedience to The Church.
In even simpler terms: the Orthospherian conviction is that "The Church is Christianity"; and any individual can only be a Christian - i.e. achieve resurrection to eternal Heavenly life - secondarily, by means of The Church.
Whereas the Romantic Christian idea is (I think) that - however things may have been in the past (and I personally acknowledge that the Altar-Civilization model used to be true); here-and-now each individual Man can and must discern Christian truth and his own salvation...
Including the discernment of which (if any) institution he regards as The True Church, and his own relationship to that Church's authority.
In the end, at bottom, ultimately; the Romantic Christian idea is that it is our individual discernment (understood as our direct and unmediated relationships with God and Jesus Christ) which is necessary for salvation; and the choice of relationship with any church (or no church) is secondary to that.
In brief; the individual (not any church) ultimately 'defines' Christianity: i.e. the way to salvation.
And therefore if, or when, that individual errs; and does not repent, and is damned; it will always be his own responsibility - regardless of whether he was following any church.
