The question I would have for you is where do you find authentic 'Catholicism?' Is it to be found in the pronouncements of the bishops of Rome or in Holy Scripture as interpreted by the earliest bishops and Catholic fathers, the creeds and the theological decrees of the universally recognized General Councils? When the first disagrees with the second, on which side should we as Catholics come down?
Canon Tallis' hypothetical question makes a necessary point that honest observation must concede. The movement of thought in modern Roman Catholic circles, including some who write apologetics aimed at converting us to their denomination, is to reject the Vincentian Canon in favor of a convoluted twist that took place in the mind of John Henry Cardinal Newman. His once balanced Anglican concept of Doctrinal Development morphed, after he became Roman Catholic, into something as dangerous as an open Canon of Scripture. The idea of "progressive revelation" is abhorrent if we call it that, but it can sound acceptable when it is given a more academically impressive name. Initially, the Magisterium in Rome rejected Newman's peculiar theory of Doctrinal Development. But, under pressure from a pope who wanted to redefine his role even further than centuries of innovation had rendered it, they were forced to accept Newman's theory, howbeit unofficially. The new "ancient" doctrine of Infallibility was created in 1870 to augment the papacy. The papal office, in previous centuries, had been embellished by forced and awkward Biblical interpretation, selected readings wrenched from their historical and literary contexts, and well-established forgeries. But, even so, they resisted the theory of Doctrinal Development that ran counter to Quod ubique, quod semper, quod ab omnibus creditum est, until they realized that Newman's rationalization was the only defense for their newest "dogma." The 1870 stretch (my proposed name for Papal Infallibility) would simply snap off and break under the strength of Vincentian tension. Bold measures were called for, and Newman's new DD fit the bill.
Contrary to this line of thought, as Anglicans, our so-called "450 year-old experiment" is not an experiment at all, but a sincere attempt at fidelity to Antiquity-above all Scripture as the Universal Consensus of Antiquity when the Church recognized the word of God, that is, the Master's voice (John 10:27).
What, then, are the real experiments?
1. Universal Jurisdiction is an experiment that failed the first time a Roman Patriarch tried to assert Roman authority in a functioning and perfectly well-established patriarchate beyond Rome's proper jurisdiction (Constantinople). That experiment failed when the Church's alleged seat of unity caused the Great Schism (1054). We are told this is a largely symbolic date; but, the symbolism was certainly a felt reality. Four of five patriarchs said no, and no one has patched the Church back together since.
2. The Crusades were another failed experiment. In the words of Pope Urban II (1042-1099):
"I, or rather the Lord, beseech you as Christ's heralds to publish this everywhere and to persuade all people of whatever rank, foot-soldiers and knights, poor and rich, to carry aid promptly to those Christians and to destroy that vile race from the lands of our friends. I say this to those who are present, it meant also for those who are absent. Moreover, Christ commands it."
He said also:
"God has conferred upon you above all nations great glory in arms. Accordingly undertake this journey for the remission of your sins, with the assurance of the imperishable glory of the kingdom of Heaven...All who die by the way, whether by land or by sea, or in battle against the pagans, shall have immediate remission of sins. This I grant them through the power of God with which I am invested."
Of course, it is a foul with 15 minutes in the penalty box to remind anybody that this heresy (for that is what Pope Urban was teaching: Heresy) was once pronounced by a pope in Rome. Too bad the ignorant illiterate masses knew nothing of Scripture and of St. Vincent's Canon. I am not quite sure where this fits in with Development of Doctrine and Infallibility; perhaps all true developments require a wrong turn along the way, making this another proof of real infallibility, not your dime-store variety that any Baptist preacher might claim.
3. Required clerical celibacy is a failed experiment, dating no earlier than the 12th century (no matter what some unheard of councils lacking ecumenical status may have said: "The Council of Toledo, held in back of the local Walmart, taught..." Save it). The result would have been a real clergy shortage, enough to sink the whole ship, if not for the help of predatory sexual perverts and other psychological misfits swelling the diminished ranks a bit.
I could go on about new dogmas, which show, by their late definition, that "progressive revelation" rather than Antiquity and Universal Consensus has ruled the roost. There are many things in the Roman Catholic Church that are very good; and we pray for true unity in the whole Church. But, if we are going to weigh the Vincentian Canon against Newman's theory of Doctrinal Development, these facts are as glaring as ever, despite tons of wasted e-ink and other sophistry. And, if we are going to ask, just who has been experimenting with failed results? - the answer seems clear.
For now I am content that to say that quite a lot of what is taught and practiced in Roman Catholicism requires a kind of Doctrinal Development. But, wherever doctrine develops contrary to Scripture, or merely without Scriptural foundation, it is always in opposition to "what has been believed everywhere, always and by all."
Quod ubique, quod semper, quod ab omnibus creditum est.