Besides the type of unity being the issue, and what really exists under sola ecclesia, what is missing is that in both cases the individual determines both which authority they will submit to as supreme, including which church, and what that authority means.
The convert to Rome makes a fallible decision to trust in a (purportedly) infallible authority, and then determines which teachings are infallible, versus those that may contain some error, or change, and the meaning of them, to varying degrees.
He can appeal for help from the general magisterium, though these are not assuredly infallible.
And he has liberty to make judgments on things the church has not spoken on or clearly taught.
The one who holds Scripture as infallible and supreme has at least as much assurance that the body of teachings he holds to are all infallible as the RC does for the body of teachings he holds to from his supreme authority, though he has no infallible list of them all.
The one under Scripture also makes judgments as to the meaning of its teachings to to varying degrees. He is to appeal for help from the general magisterium, though these are not assuredly infallible.
Thus under both Scripture as supreme and the church as supreme individuals determine which infallible authority they will hold to as supreme, and engage in interpretation of them, but not as possessing assured infallibility and superior to them.
(Note however that the magisterium is upheld, but not as assuredly infallible, though they may and will teach truths that are without error.)
The question is which is Scriptural?
Does an office making an infallible judgment mean all like judgments by its successors will be infallible?
How do we know the NT church made infallible judgments? Because Scripture records them or because for the first time an office in scripture an office possessed assured formulaic infallibility?
Did souls submit to Christ because they judged Him worthy of faith based upon Scriptural substantiation, or because they were following a magisterium as infallible?
Was an infallible magisterium necessary for writings to be established as Scripture?
Did being the instrument and steward of Divine revelation require or mean they were assuredly infallible, as Rome claims for herself?
Is unity based upon implicit trust in an office of men, which cults also example, Scriptural and superior to unity based upon the Berean heart and method, even though it allows for competition and requires truth be established by overcoming evil with good?
The point was that sola scriptura is unworkable, fails, to result in "one Lord, one faith, one baptism".. If you're conceding that and popping up another mole... :)
The question is which is Scriptural?
That's the second point, sola scriptura is unscriptural. It is incumbent upon sola scriptura to pass its own test, the Church doesn't hold this doctrine so it does not apply it. I don't see where scripture alone for all dogma and doctrine is scriptural.
Your discussion of infallibility, I find the use somewhat nonsensical. Does your Church claim its dogma and doctine is fallible?
If you are talking about papal infallibility, then we need to be clear about that; I'm not sure which you're referring to.
thanks for your reply.
The convert to Rome makes a fallible decision..
I think we could list two of the possible choices: Find the true Church and follow its teaching. Decide the true teaching and follow the church that teaches them.
There are other possibilities for an individual seeker; but this is still removed from the topic of sola scriptura and whether it is workable in practice or passes its own scriptural test.