This really all boils down to the development of doctrine. No, Mickey, Papal Infallibility was not clearly explicated in the first millennium, just as the nature of the procession of the Holy Spirit was not clearly explicated in 175 AD. But the core of the belief has always been there, since Apostolic times, both in the case of Papal infallibility and the procession of the Holy Spirit.
I ardently agree with the above quote. This is what it all boils down to. If I can be personal for a moment, I reckon that if my beliefs on the development of doctrine were not in line with Catholic teachings, then Orthodoxy might be an appealing option

Fortunately, I have no such scruples.
I’ve read over the Orthodox position regarding their rejection and, for me, their reasoning seems rather inadequate.
In 1895 the “Reply of the Synod of Constantinople to Pope Leo XIII” reads in its 24th Chapter:
“It is manifest that the universal Church of God, which holds fast in its bosom unique, unadulterated and entire this salutary faith as a divine deposit, just as of old it was delivered and unfolded by the God-bearing Fathers moved by the Spirit, and formulated by them during the first nine centuries, is one and the same forever, and not manifold and varying with the process of time: because the gospel truths are never susceptible to alteration or progress in the course of time, like the various philosophical systems; ‘for Jesus Christ is the same yesterday, and today, and forever.’ Wherefore also the holy Vincent [of Lerins] who was brought up on the milk of piety received from the Fathers in the monastery of Lerins in Gaul, and flourished about the middle of the fifth century, with great wisdom and orthodoxy characterizes the true catholicity of the Faith and of the Church saying ‘In the Catholic Church we must especially take heed to hold that which has been believed everywhere, at all times, and by all. For this is truly and properly catholic, as the very force and meaning of the word signifies, which moreover comprehends almost everything universally. And this we shall do, if we walk following universality, antiquity, and content.’ But as has been said before, the western Church, from the tenth century onwards, has privily brought into herself through the papacy various and strange and heretical doctrines and innovations, and so she has been torn away and removed far from the true and orthodox Church of Christ. How necessary it is, then, for you to come back and return to the ancient and universal doctrines of the Church…”
The Eastners quote from St. Vincent of Lerins, but in the very same work St. Vincent notes:
"But some one will say, perhaps, Shall there, then, be no progress in Christ’s Church? Certainly; all possible progress. For what being is there, so envious of men, so full of hatred to God, who would seek to forbid it? Yet on condition that it be real progress, not alteration of the faith. For progress requires that the subject be enlarged in itself, alteration, that it be transformed into something else. The intelligence, then, the knowledge, the wisdom, as well of individuals as of all, as well of one man as of the whole Church, ought, in the course of ages and centuries, to increase and make much and vigorous progress; but yet only in its own kind; that is to say, in the same doctrine, in the same sense, and in the same meaning.
The growth of religion in the soul must be analogous to the growth of the body, which, though in process of years it is developed and attains its full size, yet remains still the same. There is a wide difference between the flower of youth and the maturity of age; yet they who were once young are still the same now that they have become old, insomuch that though the stature and outward form of the individual are changed, yet his nature is one and the same, his person is one and the same. An infant’s limbs are small, a young man’s large, yet the infant and the young man are the same…"
Im sure some of our Orthodox brethren can more fully explain to us their beliefs regarding Dev. of Doc.
God bless,
JJR