I do not think that it is I who err. It is the Council itself that said its condemnations were in accord with Agatho's letter, including with respect to Honorius:
"...in accordance with the sentence already given concerning them in your letter, and their names are these: Theodore, bishop of Pharan, Sergius, Honorius, Cyrus, Paul, Pyrrhus and Peter..."
The Council said its condemnation of Honorius was in accord specifically with the sentence given on Honorius in St. Agatho's letter. However, St. Agatho does not mention Honorius by name. He does say the Apostolic see has been free of error, and that his predecessors opposed the heresy, at least through 'silence.' Thus, Agatho grouped Honorius with his orthodox predecessors - so as the Council said its judgements were in accord with said letter, we must conclude the Council agreed with Agatho - unless YOU want to assert the Council was in error.
The only grounds the Council had in Agatho's letter is the opening he gave them - clearly with Honorius in mind - that "woe" to one who should 'cover over the truth with silence.' As Agatho had said his predecessors were orthodox - the only grounds left to the Council was to condemn Honorius, as Agatho indirectly did, on the grounds that Honorius, even though personally orthodox, had covered over the truth through silence...by 'defining nothing' - as he said in a letter to Sergius.
Further, on this point, the emperor's letter is consistent with this analysis. In his edict re the council, the emperor states:
"...The heresy of Apollinaris, etc., has been renewed by Theodore of Pharan and confirmed by Honorius, sometime Pope of Old Rome, who also contradicted himself...."
We see here clearly stated that Honorius "contradicted" himself. What, therefore, was his contradiction? It certainly could not be that he was a heretic who expressed himself heretically; but rather, that he was orthodox but failed to defend it!
You are arguing from silence, or perhaps the placement of a period (which may or may not have been there in the original Greek Acta -- I am unable to find a source for the Greek Acta online and even if I did, unless it indicated that it used the original punctuation, rather than modernizing it, a matter of controversy among Byzantinists, it wouldn't settle the matter), in claiming that because the Holy Fathers did not repeat the phrase "minded contrary to our orthodox faith" in their condemnation of Sergius and Honorius, that the relevant distinction is between those explicitly so described in one sentence and those condemned "with these" in the following sentence beginning with "And", rather than between those suggested for condemnation by St. Agatho in his letter and those found heretical by the Council's own examination.
Yours is an amazing assertion! I am not arguing from silence. I have cited St. Agatho, St. Leo II, St. Maximus, John IV, the Acts of the Council, the Council's letter to Agatho, and now the Emperor - all showing that the case I am making is consistent, and that it alone reconciles all the known data points. You only want to cite the Council in isolation without wanting to reconcile all the data to your hypothesis.
I suspect there is really not much point in continuing our discussion. Each of us arguing for a position the other, due to his ecclesiological commitments, regards as completely unsupportable. I seem to recall that in a similar circumstance the discussions between the Patriarch of Constantinople and the Lutherans at Tubingen ended with a request from the former to cease writing about doctrinal matters, and write only for the sake of friendship. Perhaps we should end in like manner.
No, indeed, there may be no more point in continuing. That said, I find your response above, respectfully, intellectually speaking, a dodge. What you say is not true. Your "ecclesiological commitments" do not require you to reject my defense of Honorius, because even if my defense is valid (and I believe it is), that in itself is not a proof of papal infallibility. So, it sounds to me as if you are copping out - making an argument from prior 'commitments' and not one from the facts of the case.
Certainly, you must see, that you could, hypothetically, admit the case I am making regarding Honorius, and that, in itself, would not prove papal infallibility or make you a "papist." Certainly, you could accept the case I am providing as at least possible without having to come close to admitting the doctrine of papal infallbility.
Interestingly, it is only by ingoring all this evidence that you can hope to maintain your erroneous view that the case of Honorius disproves papal infallibility - which essentially was your initial assertion, if I recall correctly. I've made a case from the overall record, without cherry picking the Council in isolation; and having done so, find your original assertion, respectfully, without merit, and purely polemical, based on your self-admitted 'ecclesiological commitments.' Regards.
It is, however, Honorius himself, who proposes, after a brief exposition of Chalcedonian Christology as regards the natures of Christ, that "It follows that we confess one will of Our Lord Jesus Christ" (Allen's translation, with which my bad school Greek finds no fault). Nor is this a mere passing phrase. Later Honorius gives what is plainly a monothelite exposition of "I did not come to do my will, but the will of the Father who sent me" and "Not as I will, but as you will Father," and similar sayings of Our Lord, in which the Pope does not take them at face-value as pointing to Christ's human will, but, of which Honorius instead writes, "these are not expressions of a different will, but of the economy of the humanity which he assumed." (Again, Allen's translation, with which I, again, agree.) This is not silence, but the statement of an erroneous doctrine.
This leaves you with the fallback position taken by Baronius that the Greek version of Honorius's letter to Sergius is fraudulent (no Latin version is extant, though I'm unclear whether that is because it is lost, or because there was only ever a Greek version -- Western churchmen in the seventh century were still often fluent in Greek). And if you really take that position, then as Patriarch Jeramias wrote to the Lutherans, pray do not write again about doctrinal matters, and if you must write do so only for the sake of friendship.
As to St. Agatho's letter, the comments on the Church of Rome not having fallen into heresy can be harmonized with the manifest profession of heretical Christology in Pope Honorius's letter, condemned as such by the Sixth Ecumenical Council, in another way than that which you propose: Honorius died before he had a chance to become not merely a heretic, but a heresiarch, leading the whole Patriachate of Rome into his Christological error as Dioscorus led the (bulk of the) Patriachate of Alexandria into his. Of course, this resolution requires that the usual metonymic identification of a see with its occupant be recognized as a poetic device, rather than an ecclesiological fact, something I know you Latins are unwilling to do, since on it rests the identification of the successors to St. Peter in the see of Rome with Peter himself.