Defenders of Roman Catholicism often argue that holding to sola Scriptura - that Scripture is the only assuredly infallible authority on faith and morals, and formally or materially sufficiency in that realm (all other material helps being subject to it - leads to doctrinal anarchy. To this it sets Rome in contrast as possessing uniformity, and which is based upon "sola ecclesia," that the assuredly infallible magisterium is effectively the supreme authority. However, in addition to the latter means being cultic, the boasting of Roman Catholics as having doctrinal unity is limited of infallible teachings, this is not what it is conveyed to be, while unity by the assent of faith which these require is inferior in quality to that of souls being persuaded by Scriptural means, even with the risks that must allow.
In comparing the two, it can be seen that overall SS type churches, who in practice hold to the supremacy of Scripture and its basically literal hermeneutic (evangelicalism) — not that of a man or an office —
overall hold to and have held to many core teachings, including those
which we agree with Rome on (as in the A. creed), due to their degree of Scriptural warrant and corroboration. You will not get far in the world's largest Prot. denom (S. Baptists) or even the Assemblies of God or Calvary Chapel, etc, if you deny such things as the virgin birth, the blood atonement for the forgiveness of sins and other facts of the gospel, the Trinity, etc., and salvation by grace versus preaching one morally earns salvation.
This doctrinal unity is shown in a common front against cults which deny such things, and against teaching as dogma "the tradition of the elders" (Mk. 7:3,5) that fail of scriptural warrant. And while disagreement is allowed in less central doctrinal areas, this is typically limited in scope, with those who exceed such being marked as aberrant by a majority. All this without a central earthly authority, which itself is not contrary to Protestant doctrine, and does exist in denominational levels, but would require such to be realized Scripturally, in accordance with its qualifications and manner of establishing spiritual authenticity and authority, which does not rest on formal decent but the power of God. (Mt. 3:9; mk. 11:28-33; Jn. 8:39,44; Rm.2:28,29)
And due to the power of the "the gospel of the grace of God," (Acts 20:24) evangelicals realize a unity of the Spirit as they walk therein, Christ in them and they in Christ, (Jn. 17:23) which transcends denominations, and is greater than their differences. Whitefield and Wesley contended with each other often strongly over predestination (Rome also had its counterpart: http://en.wikipedia.org/wiki/Congregatio_de_Auxiliis),
yet could share each others pulpit at times, both preaching the
gospel of salvation by God's grace, not appropriated by man moral
deserving it (as what mean earns is damnation), which effects
manifest transformative regeneration. And as a result of this
essential common bond, based upon a common Scripture-based
conversion and relationship, such believers can realize spontaneous
fellowship as well as in formal gatherings and ministries
Meanwhile, RCs also must hold to a few core truths, giving assent of faith to infallible pronouncements, but which requires interpretation in discerning how many of the multitudes of potentially infallible teaching really are, and which themselves can vary in interpretation, while Roman Catholics are allowed varying degrees of dissent in non-infallible teachings,
(http://www.catholicplanet.com/TSM/general-magisterium.htm) which comprise the bulk of what RCs believe and practice. Yet this also is a matter of some interpretation.
In addition, unlike evangelicals which produced extensive commentaries on the Scriptures, Rome has not only infallibly defined very few texts - how many being also a matter of
interpretation - but has historically suppressed Biblical literacy
and and has little in the way of extensive analysis of Scripture,
while its own approved commentary on Scripture in the official Bible
for America (NAB) is critically liberal.
Moreover, evangelicals today, even in our compromised state, evidence greater conservative unity in many core truths and moral views than their RC counterparts, who are
widely divisive, even among clergy, or of those in like
institutionalized faiths. (http://www.peacebyjesus.com/RC-Stats_vs._Evang.html)
This should not minimize the import of divisions, but provide some perspective in its effects. And if unity is itself the goal of the Godly, then cults would be supreme, while division because of truth, (1Cor. 11:19) is greater than unity in
Finally, both systems, that of sola ecclesia and Sola Scriptura, you have an infallible authority which is subject to fallible interpretations, but Rome' claim to be so is effectively based upon her own self-proclamation — she decrees
something according to her infallible criteria and therefore it is —
while Scripture became progressively established as such not by
conciliar ecclesiastical decree, though they can be helpful (and it
toll Rome over 1400 years after the last book was written to provide
an “infallible canon: http://peacebyjesus.witnesstoday.org/Ancients_on_Scripture.html#2), but due to its unique heavenly qualities and effects, and other manifest supernatural attestation by God, and the complementarity of its contents. And it is by the “manifestation of the truth” that souls are to be persuaded, as in Scripture, (2Cor. 4:2; 6:1-10; Heb. 2:3,4)