"Similarly, would not the need for precision lead us to say "the majority of Orthodox theologians today do not accept the teaching of the Immaculate Conception" rather than "Orthodoxy does not accept ..." ? This would indicate that the Immaculate Conception could still be an orthodox opinion within Orthodoxy. I fear that the simple statement "Orthodoxy rejects ..." can feed into an anti-Roman reaction that uncritically considers as heretical any opinions that Catholics hold that is seem to originate outside the Orthodox consensus."
I suppose that if Orthodoxy and the Latin Church were able to agree on the basics of man's state before and after The Fall and arrive at a place different from where +Augustine's notions have lead the Western Church, I'd agree. There is absolutely no question, so far as I know, that both the Latin Church and Orthodoxy hold, in accord with the consensus patrum, that Panagia was ever sinless. How she got that way is the issue. If the West believes that she was preserved by some special, or rather, unique grace as opposed to believing that she responded fully to the very same grace which is available to all of us, and explain the Immaculate Conception that way, then we still have the same problem and such an idea couldn't even be theologoumennon in Orthodoxy. This of course points to that most arcane of theological questions, created versus uncreated grace, something which can tie our brains into knots!
P, absent an acceptance of Original Sin, I cannot see how any Orthodox person could accept the Immaculate Conception even as theologoumennon. Some Orthodox writers may have used the term Immaculate Conception, but if they accepted the usual understanding of that term, then they were outside Orthodox teachings on the issue. I remember hearing an Orthodox Metropolitan once speak about the Immaculate Conception as if it were an Orthodox doctrine. Afterwards I spoke with him about it and his explaination showed that while he had a fine understanding of the Orthodox position, it hadn't a clue what the Latin Church meant by the term. In fact, it shocked him that given the true meaning of the term, he had been using it all wrong.
"I fear that the simple statement "Orthodoxy rejects ..." can feed into an anti-Roman reaction that uncritically considers as heretical any opinions that Catholics hold that is seem to originate outside the Orthodox consensus."
There is always the danger of claims of heresy, even when it isn't actually there, especially among those who are not fully conversant with the subject. Its one thing to say that some theological opinion is rejected, quite another to say it is heresy. Recently, either here or on another site, commented that a reason the Pope proclaimed the dogma of the Immaculate Conception was to combat a "heresy" that Panagia had sinned. This is of course absurd (smacks of the filioque, doesn't it?)as no one has made any move to anthemize +John Chrysostomos as a heretic so far as I know. Now your comment that the words "Orthodoxy rejects" could feed into anti-Roman sentiment is well taken. There still is some of that among the "cradle" Orthodox faithful, but in all honesty, virtually all of it has died out in the past 30 years or so. Where I see most of it is in converts from Western Protestantism who for at least a time after conversion (5-10 years)seem to carry a heavy load of anti-Catholic baggage. Thank God that usually goes away, not because they become more accepting of Latin theological positions, but because those positions simply have no meaning in their lives as Orthodox Christians.