Valentinus #1
How do we defend Catholic doctrines, such as Filioque or Petrine Primacy?
Note that the early Church always accepted the Bishop of Rome as head of the Church. In about 80 A.D., the Church at Corinth deposed its lawful leaders. The fourth bishop of Rome, Pope Clement I, was called to settle the matter even though St. John the Apostle was still alive and much closer to Corinth than was Rome. Tradition shows Pope St Clement exercising his primacy in about 96, on this schism in the Church of Corinth.
The Orthodox are closest to Catholicism but:
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787. Apart from their rejection of Papal Infallibility, has purity of doctrine from the Catholic point of view been maintained by the Eastern Orthodox Churches?
Not entirely. Besides denying Papal Infallibility they would, of course, deny Papal Supremacy. They grant that the Pope has a primacy of honour, but not that he has supreme jurisdiction over the whole Church. They deny, also, the dogma of the Immaculate Conception of the Blessed Virgin Mary as regards her exemption from original sin, although holding that she was ever personally sinless. In cases even of a valid marriage they permit divorce and remarriage.”
radioreplies.info/radio-replies-vol-5.php?t=15&n=787
"…many Orthodox theologians and bishops have now severely qualified or even surrendered any serious claim to infallibility on the part of their Church. Also, there is no longer any unity, any identifiable “official” position of Orthodoxy as such, in regard to unnatural methods of birth control. Some authorities continue to reprobate these practices, while others – probably the majority by now – condone them. Increasingly, Orthodox married couples are advised just to follow their own conscience on this issue.
“…in recent decades, with more extensive cultural and ecumenical contacts, and with an increasingly large and active Eastern diaspora in Western countries, Orthodoxy’s underlying vulnerability to the same liberal and secularizing tendencies in faith, morals and worship that have devastated the West is becoming more apparent. That virus – **an inevitable result of breaking communion with the visible ‘Rock’ of truth and unity constituted by the See of Peter **– is now inexorably prodding Orthodoxy toward doctrinal pluralism and disintegration.” [My emphasis].
rtforum.org/lt/lt133.html#Harrison