Ah, an Ecumenical Council.... What a glorious vision, the dream of having one again!
We shouldn't forget history. As St. Gregroy Nazianzen said:
"To tell the truth, I am convinced that every assembly of bishops is to be avoided, for I have never experienced a happy ending to any council; not even the abolition of abuses ..."
Ecumenical Councils are meant to be extraordinary medicine, not nourishment or something to look forward to having. Just like many medicines, they tend to have harsh side effects--as St. Basil said, they tend to result in "shocking confusion and disorder." But over time, we see they are for our ultimate good and are necessary to preserve the faith. Councils meant to heal schism, only have a 33% success rate (the Council of Constance being the exception, and that had no doctrinal issues at dispute). Sometimes, larger schisms are effected--like what happened after Ephesus, Chalcedon, Constantinople IV, and Vatican I--and usually at least minor schisms happen.
The last two times we tried re-uniting with the East by ways of ecumenical council, things seemed to get even worse afterwords--even though we adjourned agreeing. If we had an ecumenical council today, depending on the result, we could expect some major schisms on either side by those who would see the Council as a betrayal.
As for what you suggest, the Orthodox don't believe ecumenical councils are infallible (which is how they explain their rejection of the re-union Councils). For them, Councils must be ratified by the church-consciousness. When this actually happens, no one can really say, especially since there are always groups who reject a Council, claiming their church-consciousness cannot accept it.
As for original sin, we just approach the same truth different ways. This has never been an issue as the doctrine existed without complaint for centuries before the Great schism, it was not an issue with the Eastern Catholic reunions, and it was not an issue at the large reunion Councils. It's only an issue from some fundamentalist anti-Latinists in certain circles in relatively more recent times.
As for Purgatory, there is not a whole lot that is dogmatically defined, and what is, is not rejected by the East in principle.
Concerning celibacy, the customs would be retained as they are--they would not ask us to sacrifice that venerable tradition.
And as for the Filioque, there are some Orthodox controversialists who claim it's heretical giving it a meaning we don't, but for most they see it as orthodox, just not added properly. That would probably be a non-issue, we'd both be able to use our own traditional creed.
We have to remember, we cannot compromise truth for the sake of "unity." Our first duty is to truth, for Jesus Christ is Truth. Here are some statements by a couple popes who have shown great willingness to compromise whatever can be for the sake of unity.
We must also remember this, as John Paul II said:
http://www.vatican.va/holy_father/j...ts/hf_jp-ii_enc_25051995_ut-unum-sint_en.html
The unity willed by God can be attained only by the adherence of all to the content of revealed faith in its entirety. In matters of faith, compromise is in contradiction with God who is Truth. In the Body of Christ, "the way, and the truth, and the life" (
Jn 14:6), who could consider legitimate a reconciliation brought about at the expense of the truth? The Council's Declaration on Religious Freedom
Dignitatis Humanae attributes to human dignity the quest for truth, "especially in what concerns God and his Church",
33 and adherence to truth's demands. A "being together" which betrayed the truth would thus be opposed both to the nature of God who offers his communion and to the need for truth found in the depths of every human heart.
And as Pope Paul VI said concerning watering down the papacy:
http://www.vatican.va/holy_father/p...uments/hf_p-vi_enc_06081964_ecclesiam_en.html
Are there not those who say that unity between the separated Churches and the Catholic Church would be more easily achieved if the primacy of the Roman pontiff were done away with? We beg our separated brothers to consider the groundlessness of this opinion. Take away the sovereign Pontiff and the Catholic Church would no longer be catholic. Moreover, without the supreme, effective, and authoritative pastoral office of Peter the unity of Christ's Church would collapse. It would be vain to look for other principles of unity in place of the true one established by Christ Himself. As St. Jerome rightly observed: "There would be as many schisms in the Church as there are priests." (65)