"Why would that be prejudice when it comes to us, but not when it comes to Roman Catholics?"
If we are all honest about this we must recognise that we all come to these questions with our own prejudices - Catholics included. This is why all these grand ecumenical projects are doomed to failure before they even start. None of us can dissociate ourselves from our respective phronemas, much though the ecumenists on either side would like us to do so.
I admire gbcdoj for his(her?) intellectual skills and seemingly endless capacity to bring forth reems of quotations from the Fathers to support the Catholic Faith, however, I know that they will count for nothing with you simply because you are not Catholic. The converse also applies with us of course.
When you speak of the Catholic Church needing to return to the Church of the first millenium, or the Church of the 7 Councils, it counts for nothing with us because we already know that we are that same Church. Original sin, the Immaculate Conception, the Pope as successor of Peter with universal jurisdiction - all these are doctrines which the Church has always held and we have our Scriptures and Tradition and the teachings of the Fathers and the saints as proof of this.
Similarly our ecclesiology with the priority of the universal Church over the local Church is also attested in both Scripture and Tradition and we simply see the Orthodox deviations from these doctrines as being novelties that were incorporated after the schism. We have had long enough experience with the Protestants (and many of our own people!) to detect the anti-Roman "frisson" when it appears, and understand how this can become a powerful driving force in the development of doctrine in communities that have become separated from Rome.
However, I am sure Jesus the Rock knew all this would come to pass when He named Peter as His chip off the old block, as it were. Just as He was the stone who would become a stumbling stone, Peter and his successors were always destined to replicate this on a minor scale - typology works forwards from the Cross as well as forwards to the Cross.
The bottom line is that while I consider "ecumenism" to be well-intentioned, in that it seeks to bring about the unity for which our Lord prayed, it is destined never to succeed because it is a lazy way of evangelizing. No matter how many ecumenical talks are held, or how many agreements are signed, none of them can bring a single person into the unity of our Lord's Church, because only the grace of conversion can do that. And, generally speaking, conversion does not happen for the right reasons when it takes place en masse, but happens one soul at a time as the Holy Spirit moves them.
For these reasons and others, I fully agree with you that unity between Catholic and Orthodox is most unlikely to happen and one has to wonder what re-establishment of the theological dialogues will actually achieve?
It's a stalemate. However, we are under commandment to be united and brotherly. Perhaps we do not understand what that means. It doesn't necessarily mean we have to be "married." Brothers often compete and even antagonize each other, even though their parents plead for them to be "as brothers." They are inevitably connected to their parents and can never disown each other but it doesn't mean they have to act as one or live together.
But borthers don't have to fight. Christian thing to do would be for the brothers to support and help each other, and stand united against common adversaries, and mutually respect each other's households rather than trying to make each other a clone of the other. That would unite us in Christ without ecclesiological re-union and bureaucratic and legalistic niceties.
And one more thing: keep in mind that the frustration you feel with the Orthodox is because the Orthodox are not asking for reconciliation or re-union. We are not making the overtures. We leave it up to God. On the other hand, when someone makes overtures to us, we take it that they desire to join us.