LatinTrad,
Someone's either baptized or they're not. If they are baptized, it is a sacriledge to re-baptize them. If they are not baptized, then they msut be baptized before partaking of Holy Communion.
Similarly, today, the Catholic Church does not re-baptize EO's, OO's or Nestorians who convert. Nor does she re-baptize Protestants from certain groups who did preserve valid baptism. She DOES re-baptize Mormons, however, as well as those Protestants who were not baptized according to the Trinitarian formula.
Look who's preserved the practice of the Early Councils!
The question is not this simplistic though.
Rather than simply make sweeping declarations, I think it would be valuable for the sake of mutual understanding to look at how Roman Catholic and Orthodox understandings of the sacrametns basically differ. While we can historically point to many personalities which have contributed to these differences, for the moment I will simply attempt to state the differences.
In the post-schism Roman church, the view was that grace is a created relationship, between God and a particular soul. In Orthodoxy, as was carefully expounded against the Latinizing opinions of Barlaam (who undoubtedly picked up these ideas from Italian influences), grace is clearly understood to be uncreated; and since only God is "uncreated", this would mean the grace given by the Sacramental rites (which makes them true, holy "mysteries") is an energy of God Himself...an outpouring of His Essence, which is fundamentally unknowable (a proposition which would come to be explicitly rejected by the Latins, most formally in their doctrine of the "beatific vision.")
If one accepts that grace is created (existing commonly as created "helps" or the "graces" spoken of by Roman Catholic teachers...or existing as a "habit" or "state", as it does in the case of the justified, as the same RC authorities would teach), then it is understandable how the Roman Catholic view on the heterodox use of "valid sacramental forms" could come about. According to the RCC, a valid sacrament has to have proper "matter", "form", and "intent". They believe all of these were established by Christ - IOW, they are "God given."
Given this, if it is this "God given form" which is God's ordinary, chosen instrument for "creating" this special "relation" to a particular soul, then it's understandable how one could teach that a "valid sacrament" could exist outside of THE Church (which obviously Roman Catholics identify with their communion.)
OTOH, let us look fairly at the Orthodox position. While it's obvious that the chief sacraments are "established by Christ", this has less emphasis. Rather, the Church Herself, being Christ's Body, is the "Holy Mystery/Sacrament" of God (since Christ, the Incarnate Logos, is the "Sacrament of God".) Strictly speaking then, anything the Church does is "sacramental"; this is why, while some late medieval/modern Orthodox sources will copy the Roman Catholic habit of speaking of "seven sacraments", at best this is an oversimplification which only speaks of the "chief" mysteries. Orthodoxy does not limit this number to "seven", and it cannot - for, like I just conveyed, all of the Church's activities are in favour of the salvation of souls, and communicate grace.
Moreover, this grace, is not (in Orthodox eyes) something "created"; rather, it is an assimilation of God's uncreated energy, unto the salvation of the soul. It is akin to His special presence in the Temple, which Christ is (the True Temple), and which only those who are members of Him can possibly be. Well, those "members of Christ" are what we call the ekklessia, or "the Church."
From this vantage point then, someone mimicking the exterior activities and rites to the Church, cannot have the same value as when the Church does these things. If the Church is the ultimate Holy Mystery (for She is Christ's Body, an extension of Him...branches of the True Vine, filled with the Life bearing "sap"), then the sacramental acts (which are really only a particularization of the entirity for a certain end) will only "do" what they say they "do", when the Church celebrates them. Only the Church, can accept (or expell) individuals - in fact it is for this very reason, that when a Priest (for example) is expelled from his ministry, should he not respect this, his acts are regarded as utterly void; he can no more "confect the Eucharist" (to borrow RC lingo) than he can even offer a Priestly blessing.
All of this helps explain why there is now such a variance between the Roman Catholic and Orthodox views of the sacraments - for the Orthodox, the sacraments cannot be divorced from their ecclessial context, without doing violence both to their intent, and effect. One cannot be "baptized into the Church" by those who are not acting in Her Name, and who have no interest in doing this to begin with (but rather, at best, initiating them into their own "church").
The Holy and Sixth Ecumenical Council prescribed that Nestorians, Monophysites, and certain other heretics NOT be re-baptized. The only possible coherent explanation is that those groups of heretics had preserved valid baptism (for reasons listed above). This prescription clearly contradicts (and, IMHO trumps) the opinion of St. Basil posted elsewhere on the forum. And it should for you guys too since you think Councils are the highest authority in the Church.
The problem is that your treatment of these canons is not one which takes for granted the mindset of those who formulated them - if it were, it creates an unnecessary contradiction. Why? Because, if we're citing canons/jurisrudence, then we have even older norms for receiving converts from heterodoxy, which are not as lenient...
Canon XLVI: We ordain that a bishop, or presbyter, who has admitted the baptism or sacrifice of heretics, be deposed. For what concord hath Christ with Belial, or what part hath a believer with an infidel?
Canon XLVII: Let a bishop or presbyter who shall baptize again one who has rightly received baptism, or who shall not baptize one who has been polluted by the ungodly, be deposed, as despising the cross and death of the Lord, and not making a distinction between the true priests and the false. (Apostolic Canons)
Within the Orthodox paradigm, the seeming contradiction between these ancient norms and more lenient methods of receiving converts from heterodoxy, poses no scandal or meaningful contradiction, because the substance remains the same. However, the same cannot be said for the Roman Catholic position - it simply leaves no room for the above norms.
When the Church does choose to be lenient in it's manner of reception, this is due to the perceived benefit, on the part of spiritual pastors, that this will have for the ability of the Church to more readily embrace the heterodox. Generally, "exactitude" is practiced for the same reasons - historically this has been when it was perceived that heretical groups were becoming very aggressive towards the Church, and it was important to draw a very clear line in the sand between the Church, and "not the Church." This is accutely so today, with so much confusion created by the ecumenical movement/agenda, and it's total perversion (within nominal Orthodoxy) of the real meaning of baptismal economy.
I would also like to say this, before concluding this post, to those who think it's simply "impossible" to heal and fill what was lacking in a heterodox baptism, via reception into the Church: can they tell me, really, precisely when someone receives the "infusion of grace" and "remission of sins" associated with Baptism? At which precise moment can this wonderful thing be found? When the Priest finishes the last words of the "baptismal formula"? When he helps the convert out of the Baptismal font? Of course no one can say precisely "when" this occurs...and if they pretend to, we would have every right to say this is just speculation, and has nothing in it's favour that even resembles "proof."
Given this, it strikes me as untrue to say the Church simply cannot complete those things which physically had already been imposed.
When the Church has issued lists then, of those who can be received by "economy", what She is saying at most, "validity" wise of the groups mentioned, is that the valid outward form of the sacraments exists in these groups - thus leaving something for the Church to complete, if this is how She chooses to receive converts. Without this, one could not extend any sort of "economy" as such - there has to be something to "build upon", so to speak.
Seraphim