This is a direct quote, let us see if pasting a quote warrants a thumbs down by a snake in the weeds:

5.   Fr. Boulet next presents the reader with a summary of the work of the brilliant and learned Brazilian layman Arnaldo Xavier da Silveira on the so-called Five Opinions regarding the “heretical Pope thesis.” Fr. Boulet has, unfortunately, used the unauthorised English translation as his source.


Keeping this qualification in view, let us consider each of the Five Opinions in turn, with Fr. Boulet. He writes:

1st  Opinion: “God would never allow a Pope to fall into heresy” The defenders of such opinion argue that Our Lord would never allow a Pope to fall into heresy.  For Cardinal Billot, the  hypothetical  possibility  of  a  Pope  falling  into  heresy  would  never  come  to  reality, according to the promise of Our Lord: “And the Lord said: Simon, Simon, behold Satan hath desired to have you, that he may sift you as wheat: But I have prayed for thee, that thy faith fail not: and thou, being once converted, confirm thy brethren.” (Luke XXII, 31-32).  For Billot, this promise should apply not only to St. Peter, but also to all his successors, as it was always understood by Tradition.  Against that opinion, we have the case of Pope Honorius (625-638), who was condemned in 680, by the 3rd  Council of Constantinople on account of hisletters to Patriarch Sergius, which favoured the Monothelite heresy5.  Let me quote from that council: “Having found that (Honorius’ letters) are in complete disagreement with the apostolic dogmas and the definitions of the holy councils, and of all the approved Fathers; and that, on the contrary, they lead to the false doctrines of the heretics, we absolutely reject and condemn them as being poisonous to the souls… We also state that Honorius, formerly Pope of the elder Rome, had been also rejected from the God’s Holy Catholic Church and is being anathemized, on account of the writings he sent to Sergius, where he adopted his ideas in everything, and reaffirmed his impious principles.”  Let us note that such condemnation happened 42 years after the death of Honorius.  Also, no matter what kind of judgement can be  passed  on  Pope  Honorius,  it  is  a  matter  of  fact  that  we  have  an  official  pontifical docuмent which admits that a Pope could possibly fall into heresy.  Such docuмent is from Pope Adrian II, more than 200 years after the death of Honorius: “After his death, Honorius was anathemized by the Eastern Church; but we should not forget that he was accused of heresy, the only crime that would make lawful the resistance of inferiors to the orders of their  superiors,  and  the  refusal  of  their  malicious  doctrines.”   As  we  see,  St.  Robert Bellarmine’s 1st  Opinion has reasons in favour and against it.  Thus we can say that this 1st opinion is only probable. [Emphasis in the original.]


Against this, we note the following.


a)   St. Robert Bellarmine, Cardinal Billot, along with the vast majority of theologians, held that a Pope could never become a heretic.   They were all aware of the case of Honorius.   Thus, any argument such as that developed here by Fr. Boulet is in fact an argument against those great and numerous authorities; and because of the notoriety of the case, to argue as he does here is implicitly to accuse those great men of the most facile error – viz. that they held something to be impossible which had famously already occurred.  Nobody can admit such an argument.


b)   The acts of the Council are of doubtful authenticity.   Indeed Cardinal Baronius (the greatest Catholic historian),  and  St.  Robert  Bellarmine  also, held that the acts of the Council had  been falsified  by  the  Greek  schismatics.    To  quote  these  (possibly  falsified)  acts  to  the  effect  that Honorius’s letter to Sergius was “in complete disagreement with the apostolic dogmas and the definitions of the holy councils,” is therefore rash and unnecessarily injurious to the reputation of a sovereign  pontiff,  and  furthermore,  it  is  incompatible  with  the  words  of  Pope  Leo  II,  who condemned Honorius not for teaching heresy or for believing it, but because he “did not, as became the Apostolic authority, extinguish the flame of heretical teaching in its first beginning, but fostered it by his negligence."  Indeed, as is commonly admitted by Catholic authorities, the letter to Sergius was in itself completely orthodox.   Its fault lay in its failure to condemn what it ought, in that context, to have condemned.


c)  Pope Honorius was not actually a heretic, but only fostered heresy by his failure to condemn it. Pope  Leo  II  did  not  condemn  him  for  holding  a  heretical  opinion,  but  only  in  the  sense  just expressed.

d)  Pope Honorius was not a manifest heretic, and nobody has ever claimed that he was.  Even John Chapman in the Catholic Encyclopedia admits that “Pope Honorius was much respected and died with an untarnished reputation.”  Therefore even if we were to admit the claim that Honorius really was a heretic, which we do not admit, he was certainly not a manifest heretic, and thus his case has no  bearing  on  the  question  of  the  incompatibility  of  the  status  of  “manifest  heretic”  and  the possession of an ecclesiastical office.

e)  Fr. Boulet is imprecise once more in claiming that in the words of Adrian II “we have an official pontifical  docuмent  which  admits  that  a  Pope  could  possibly  fall  into  heresy.”    This  is  simply unsupported by the text quoted, which reads, “After his death, Honorius was anathemized by the Eastern Church; but we should not forget that he was accused of heresy, the only crime that would make lawful the resistance of inferiors to the orders of their superiors, and the refusal of their malicious doctrines.”  As can readily be seen, Pope Adrian II in no way admits that a Pope really can fall into heresy, but merely comments on the actions and beliefs of others.  And this is yet another case of arguing against Bellarmine and all the rest, by claiming against them that Popes really can fall into heresy.  Which only shows that Fr. Boulet did not consider these matters in sufficient depth.  To be fair to him, in this case he has been deceived by the very poorly executed English translation of da Silveira, the error of which on this point Fr. Boulet has adopted uncritically.

Incidentally, I doubt the authenticity of that text from Adrian II, on the grounds that it appears to express erroneous doctrine on the nature of true obedience.  We certainly may resist the commands of  superiors even when they are not heretical, if they are evil in some other way.   It would be interesting to hear what SSPX thinkers say about this. That is, if heresy is truly “the only crime that would make lawful the resistance of inferiors to the orders of their superiors, and the refusal of their malicious doctrines,” then what are we to do with the (they say) non-heretical laws and doctrines of
Vatican II and its Popes?

It has been proven, under the definition of infallibility that a Pope can not be heretical, HOWEVER, it has been shown that that cleric was heretical BEFORE he was Pope.  Therefore, he would not be a Pope, invalid election.  And intention is not there so that consecration to be made a Pope can not take place.  So, by the fruits you will know them.  A manifest heretic, can not be validly elected, and can not be consecrated Pope.  That is why Ratzinger is not a Pope.  He was manifest heretical before consecration.  He showed his hereticalness at Vatican II, and his actions and books.