Speaking of the Ecumenical Councils isn't automatically the same (from what I've been taught) as assuming that all who adhere to them automatically interpret them the right way when it comes to how others are treated. Many who accepted the Council of Ephesus were not automatically correct in going out and beating up those who did not accept it because of their zeal for the Theotokos - nor were all in Alexandria correct when they went out destroying pagan temples because of their zeal for Christianity. The council may have been accurate but the actions of others are not necessarily so....as their actions can be an embarrassment.
But on Hart's Words, he did have some interesting thoughts when it came to the Fifth Council and the "embarrassment" of what resulted with others taking it past what it was meant to signify...as he said on the following:
When first presented with the universalist hope, many Orthodox and Roman Catholics immediately invoke the authority of the Fifth Ecumenical Council (553), citing the fifteen anti-Origenist anathemas: “Apokatastasis has been dogmatically defined by the Church as heresy—see canon 1 … case closed.” Over the past two centuries, however, historians have seriously questioned whether these anathemas were ever officially promulgated by II Constantinople. The council was convened by the Emperor Justinian for the express purpose of condemning the Three Chapters. Not only does Justinian not mention the apokatastasis debate in his letter to the council bishops, but the Acts of the council neither cite the fifteen anathemas nor record any discussion of them. Hence when church historian Norman P. Tanner edited his collection of the Decrees of the Ecumenical Councils in 1990, he did not include the anti-Origenist denunciations, offering the following explanation: “Our edition does not include the text of the anathemas against Origen since recent studies have shown that these anathemas cannot be attributed to this council” (I:106).
Who then wrote the anathemas and when? Over the past century different hypotheses have been advanced, but historians appear to have settled on the following scenario, first proposed by Wilhelm Diekamp in 1899 and more recently advanced by Richard Price: the Emperor Justinian and his theological advisors composed the anathemas and then submitted them to the bishops for “approval” before the council formally convened on 5 May 553. We do not know how long before the council this meeting took place (hours? days? weeks? months?) nor who attended nor whether there was any actual discussion of the anathemas. One thing is clear—the Emperor wanted the anathemas cloaked with conciliar authority. A decade earlier he had denounced apokatastasis in an epistle to Patriarch Menas. Regardless of the origin of the 15 anathemas, we may confidently affirm that the Fifth Ecumenical Council did not formally publish them. The burden of historical proof now lies with those who maintain that the Council Fathers officially and authoritatively promulgated the anti-Origenist anathemas.
But let’s hypothetically assume that the Council did publish the fifteen anathemas. There would still remain the challenge of interpretation. Not all universalisms are the same. Just as there are both heretical and orthodox construals of, say, the atonement or the Incarnation, so there are heretical and orthodox construals of the universalist hope. The apokatastasis advanced by St Gregory of Nyssa, for example, differs in critical ways from the sixth-century theories against which the anathemas were directed. The latter appear to have belonged to an esoteric metaphysical system set loose from the Scriptures, as even a cursory reading reveals. The chasm between the two is enormous. Scholar Augustine Casiday suggests that we need to think of the anti-Origenist anathemas as the rejection of this system as a whole, each anathema denouncing one of its particulars (private email correspondence). Met Kallistos Ware made a similar point in 1998:
There is, however, considerable doubt whether these fifteen anathemas were in fact formally approved by the Fifth Ecumenical Council. They may have been endorsed by a lesser council, meeting in the early months of 553 shortly before the main council was convened, in which case they lack full ecumenical authority; yet, even so, the Fathers of the Fifth Council were well aware of these fifteen anathemas and had no intention of revoking or modifying them. Apart from that, however, the precise wording of the first anathema deserves to be carefully noted. It does not speak only about apocatastasis but links together two aspects of Origen’s theology: first, his speculations about the beginning, that is to say, about the preexistence of souls and the precosmic fall; second, his teaching about the end, about universal salvation and the ultimate reconciliation of all things. Origen’s eschatology is seen as following directly from his protology, and both are rejected together. …
Now, as we have noted, the first of the fifteen anti-Origenist anathemas is directed not simply against Origen’s teaching concerning universal reconciliation, but against his total understanding of salvation history—against his theory of preexistent souls, of a precosmic fall and a final apocatastasis—seen as a single and undivided whole. Suppose, however, that we separate his eschatology from his protology; suppose that we abandon all speculations about the realm of eternal logikoi; suppose that we simply adhere to the standard Christian view whereby there is no preexistence of the soul, but each new person comes into being as an integral unity of soul and body, at or shortly after the moment of the conception of the embryo within the mother’s womb. In this way we could advance a doctrine of universal salvation—affirming this, not as a logical certainty (indeed, Origen never did that), but as a heartfelt aspiration, a visionary hope—which would avoid the circularity of Origen’s view and so would escape the condemnation of the anti-Origenist anathemas. (“Dare We Hope for the Salvation of All,” in The Inner Kingdom, pp. 199-200)
Many scholars would now question Ware’s identification of the views of Origen with the views of the 6th-century Origenists. The renowned patristics scholar Brian E. Daly, for example, asserts that the denounced theses “represent a radicalized Evagrian Christology and cosmology, and a doctrine of apokatastasis that went far beyond the hopes of Origen or Gregory of Nyssa. They envisage not only a spherical, ethereal risen body, but the complete abolition of material reality in the world to come, and the ultimate absorption of all created spirits into an undifferentiated unity with the divine Logos, so that even the humanity and the Kingdom of Christ will come to an end” (The Hope of the Early Church, p. 190). But Ware’s key point stands: the sixth century condemnation of apokatastasis does not apply to construals similar to those of St Gregory of Nyssa or St Isaac the Syrian. Consider the first anathema: “If anyone advocates the mythical pre-existence of souls and the monstrous restoration that follows from this, let him be anathema.”
Note the intrinsic connection between the pre-existence of souls and the universal restoration: the latter necessarily flows from the former, as further explained in anathema fourteen, which speaks of the eschatological annihilation of hypostases and bodies and the restoration to a state of pure spirit, akin to the original state of pre-existence. But neither Gregory and Isaac advocate the pre-existence of souls. Their construals of the universalist hope are grounded solely upon God’s infinite love and the power of purgative suffering to bring enlightenment to the damned. The 15 anathemas, therefore, do not touch the biblical universalism of St Gregory of Nyssa, St Isaac the Syrian, or more recent exponents, such as Sergius Bulgakov and Hans Urs von Balthasar. As J. W. Hanson writes in his classic, but dated, work Universalism: “The theory here condemned is not that of universal salvation, but the ‘fabulous pre-existence of souls, and the monstrous restitution that results from it'” (chap. 21).