Ok, let's break this up a little
Several. First, they simply didn't accept Chalcedon, just like later Rome would accept and then reject Constantinople IV. The part that says "I'm leaving" is the one doing the rupture.
No, it was still Rome and its followers who didn't accept Ephesus II
, a council called by the Emperor of the Ecumene, and presided by the Patriarch of Alexandria. The only reason Chalcedon even took place was because Theodosius II died and Marcian wanted to make nice with the Pope of Rome.
Second, I really don't buy all the current talk I see about "oh, we all meant the same thing, we just used different words. Those ancient guys were some intolerant stubborn fellows, but today we know better". I really don't and I think it's a very thin argument. In any serious study of history, primary sources prevail over commentaries, earlier witnesses prevail over later witnesses. Since the status is such that I have to choose between the opinion of philosophers, theologians, bishops, martyrs and saints who took part in the events, who spoke that language either as a mother tongue or a second living language, over the witness of modern specialists who have to rely on interpretation of languages they know only intellectually, I think it's more rational to conclude that the modern specialists are the ones who are been biased toward their modern cultural prejudices and ecclesiological ecumenist agendas.
Thus, considering the witness of the events of that time and of subsequent events, Non-Chalcedoneans spoused a divergent doctrine. Notice that this analysis of historic events only, the content of the doctrine is irrelevant here. We had occasions where just few Christians spoused Orthodox doctrine and heterodox had all the major "jobs". But comparing to what existed before, and what came after we can see that Orthodox doctrine always prevailed in all the Ecumene. Non-Chalcedonean doctrines, much like Rome's, never went beyond their own cultural area. In fact, the only difference between them and Rome is that European countries went on imperialistic spree in the second millenia, expanding its own social borders, but never it's doctrines gained really culturally ecumenical acceptance like the Orthodox which you can find in European, Middle Eastern and Asian cultures.
First, they did not espouse a "new doctrine", they espoused the same old doctrine which was made synonymous with St. Cyril, who if you remember, was the one who presided over the 3rd Ecumenical council. It is in fact the Chalcedonian party who introduced new doctrine to the fore.
Secondly, saying we profess the same faith now is not the same as saying we have always professed the same faith. I personally do not think all Chalcedonians were Orthodox until Second Council of Constantinople, when all elements of Nestorianism were finally purged.
Thirdly, the reason we could not "escape our boundaries" was because Rome decided to take up its old sport of persecuting the Orthodox again. We barely stayed alive during that time, and yet you could not kill us.
Finally, the whole dispute was done in Greek. Greeks tend to know what they mean in Greek better than non-Greeks. Non-Chalcedoneans and Rome simply break with Greek linguistic tradition to argue what Greek words mean or not. *If* as modernists say, it was just a matter of words, Chalcedon simply arbitrarily created a dictionary entry for the word: this is what the technical meaning of this word in theology will be from now on. Let's go past that. To break communion because of disagreement on which word to use would be a more frivolous motive than actual doctrinal difference.
Ok this really grinds my gears. The Hellenes living in Alexandria and Antioch at the time were in fact just that, Hellenes or "Greeks". To claim that they were not is plain historical revisionism. Secondly, it was Leo who broke communion with the Orthodox because we didn't like his letter enough. That is basically the very definition of hubris and that's the person you guys decided to follow. We continued in our Orthodoxy, you left it.
So: Non-Chalcedoneans broke from of the Roman-Hellenic traditions and linguistic culture of the epoch. Non-Chalcedoneans either had different doctrines as the witnesses of the event and soon later on claim, or broke away out of frivolous attachment to word definitions like modernists claim. Non-Chalcedoneans started as and remained an Oriental thing... in scientific parlance, their "theory" never went past peer-review remaining a fringe theory of a closed group who refuses to accept tested theories.
Said that, I do not judge character or piety based on that. Virtues and vices, fortunately, are more or less equally distributed among all groups.
1. Not true, there were just as many "non-chalcedonians" belonging to the Empire as were outside it, at least for the first century after the schism. It was only after the persecutions that this changed.
2. Not true, we stayed true to the doctrine as prescribed by the Fathers of Orthodoxy, repeating this canard over and over again will not make it true.
3. As I said above, Rome persecuted the Orthodox in the centuries before the Councils, it resumed in the centuries afterward. The fact that we survived at all is a miracle from God.