Unity in faith is a great good thing
But because we do not believe the same things we cannot share communion.
Are Orthodox united in the belief expressed in the Holy Scripture that slaves should be subject to their Masters?
Ephesians 6:5
Slaves, be obedient to them that are your masters according to the flesh, with fear and trembling, in singleness of your heart, as unto Christ.
Colossians 3:22
Slaves, obey in all things your masters according to the flesh; not with eyeservice, as menpleasers; but in singleness of heart, fearing God.
1 Timothy 6:1
Let as many slaves as are under the yoke count their own masters worthy of all honour, that the name of God and his doctrine be not blasphemed.
Titus 2:9-10
Exhort slaves to be obedient unto their own masters, and to please them well in all things; not answering again; Not purloining, but shewing all good fidelity; that they may adorn the doctrine of God our Saviour in all things.
1 Peter 2:18
Slaves, be subject to your masters with all fear; not only to the good and gentle, but also to the froward.
Of course, I suppose that today all Orthodox do believe that slavery is wrong. However, it was not always so in the past when Orthodox clergy held slaves and believed that it was permitted by Holy Scripture. This occurred more recently, in Romania for example, with the gypsies, but I suspect it was also the case in the time of St. Paul and slightly later.
What is the point. The point is that even though Orthodox clergy and laypeople were not united in the belief of the evil of slavery, still there was sharing of Holy Communion between the two who had opposing views on this issue.
So I believe it is false to say that there cannot under any circumstances be sharing of communion if there is not complete union in what you believe to be right or wrong.
And to take a more contemporary issue, the issue of artificial birth control, there still are some Orthodox clergy who do not accept it.