Greetings in that Divine and Most Precious Name of Our Lord and Savior Jesus Christ!
A serious problem with Catholics becoming Orthodox is that at some point the person is going to look in the mirror and say "The Catholic Church cannot have Apostolic Succession and valid sacraments...If they do then I converted for nothing!!...and THAT cannot be possible!"
That kind of black and white thinking is very destructive to both the individual and to corporate perceptions of what is true and what is not.
It is the kind of thinking that our bi-lateral discussions are eventually going to need to address.
The entire problem with ecumenism today and in the past is that folks on all sides of the discussions have the obvious bias that they inflect their own jurisdictions to be the only valid jurisdictions. Now in the 5th century after "legalization" of Christianity we began this silly fight for supremacy within the Churches, be it from Roman instigation or Constantinople, or when Alexandria decides to be the self-proclaimed boss, or what about those pesky Nestorians hiding in the environs of Syria? The reality of the matter is that we either reinvent Orthodox to say, "Only one jurisdiction is the correct jurisdiction" or we learn what the Fathers believed BEFORE any schisms found their way into the Universal Church.
Why is it the Universal Church? Simply because the Grace of the Divine Mysteries/Sacraments transcends
geography, politics, or theological disputation. This is what the Fathers implied with a Universal Church, that despite any human differences, the Church remains what it is across time and space and beyond. In the Kingdom of God and here on the Earth, there is ONE Church, just as there is ONE God, and yet clearly history has shown that like our Triune God is manifested in Three Persons with One Source, so to has our ONE, UNIVERSAL Church been manifested into multiple jurisdictions with God as our unifying Source.
The first four hundred years of Christian fathers didn't seem to have as much of a line in the sand
problem about this as we do since the first schisms. We used
to fellowship as equals, despite our variable differences.
The solution today? To readjust to the initial attitudes of the fathers, and to again learn to respect each other as equals. This means Romans and Byzantines should stop vaunting over the rest of Christendom, and we Oriental need to come off our high horses as well.
We obviously had several differences before any Schisms, but these were only exasperated when they were codified and institutionalized as such in the process of Schism.
Heresy is a strong appellation, and rightfully belongs to some rogue or renegade priests and theologians who misguide their flocks, but clearly after so many hundreds of years of continuation, we can all agree that whether RC, EO, or OO, it is hard to attribute our differences solely to a few bad-apple heretic priests and bishops leading the flocks astray as in other heresy movements which collapse under their own inherent falsehoods. Rather, time and history has demonstrated as we always knew, the Church is a Body with several connected body parts each with their own important function, and these body parts are the jurisdictions.
I say the Catholic Sacraments are valid for those called to be Catholics, the Byzantine Mysteries are valid for those called to be Byzantine, and the Oriental Mysteries are valid for those called to be Oriental, however if we keep sticking our tongues out and jeering at each other like children in the back seat of the family station wagon then surely we will just continue to look as silly as that. We should not try to convert or preach to other jurisdictions aside from the spirit of fellowship. We should not then suppose that these other jurisdictions are invalid and open territory as this utterly disrespected these already established communions. Rather, its just as the Apostle Paul taught us by his example in Romans 15
"It has always been my ambition to preach the gospel where Christ was not known, so that I would not be building on someone else’s foundation. Rather, as it is written:
“Those who were not told about him will see,
and those who have not heard will understand.”
This is why I have often been hindered from coming to you."