I have followed with interest the discussion over the recent conversion of Professor Robert C. Koons to the Catholic Church. There is a particularly insightful article by Dr Adam Cooper, Another Big Fish, at First Things.
Some of the comments can be equally applied to Anglicans who have swum the Tiber or over the discussion on the Motu:
Koons has some salient points to make on sola scriptura as well. In Lutheran teaching, each individual believer is obliged to attach him- or herself to an orthodox congregation, using Scripture alone as an evaluative norm. But this, says Koons, is “an impossible burden.” In contrast, “on the Roman Catholic view, the individual believer can recognize the true church, not only by examining its doctrines one by one, but also by investigating its historical connection (via a physical and social chain of transmission) to the apostles.” Koons does not want to his readers to escape their individual responsibility. His point is simply that doctrinal fidelity cannot be separated from institutional unity as a mark of catholicity.
In other words, the context is important. The issue, for Catholic Anglicans, is not sola scriptura but rather an idea of sacramental validity. Again, to remove this outside of the context of the Church, the institutional unity, is theological insanity. Context defines, to some extend, theology.
This is also an important issue to remember in any discussion on the Motu and the wider use of the Traditional liturgical rite: Language does not make the liturgy holy, but the liturgy the language.