Bishop Athanasius Schneider: “There is no authority to declare or consider an elected and generally accepted Pope as an invalid Pope. The constant practice of the Church makes it evident that even in the case of an invalid election this invalid election will be de facto healed through the general acceptance of the new elected by the overwhelming majority of the cardinals and bishops.” [Schnieder’s Article | My Commentary]

Cardinal Billot: “Finally, whatever you still think about the possibility or impossibility of the aforementioned hypothesis [of a Pope falling into heresy], at least one point must be considered absolutely incontrovertible and placed firmly above any doubt whatever: the adhesion of the universal Church will be always, in itself, an infallible sign of the legitimacy of a determined Pontiff, and therefore also of the existence of all the conditions required for legitimacy itself. It is not necessary to look far for the proof of this, but we find it immediately in the promise and the infallible providence of Christ: ‘The gates of hell shall not prevail against it,’ and ‘Behold I shall be with you all days.’ For the adhesion of the Church to a false Pontiff would be the same as its adhesion to a false rule of faith, seeing that the Pope is the living rule of faith which the Church must follow and which in fact she always follows. As will become even more clear by what we shall say later, God can permit that at times a vacancy in the Apostolic See be prolonged for a long time. He can also permit that doubt arise about the legitimacy of this or that election. He cannot however permit that the whole Church accept as Pontiff him who is not so truly and legitimately.

“Therefore, from the moment in which the Pope is accepted by the Church and united to her as the head to the body, it is no longer permitted to raise doubts about a possible vice of election or a possible lack of any condition whatsoever necessary for legitimacy. For the aforementioned adhesion of the Church heals in the root all fault in the election and proves infallibly the existence of all the required conditions.” [Source of this quote: an article by Robert Siscoe here]

Vigano: “In 1378, after the election of Pope Urban VI, the majority of Cardinals, Prelates and the people recognized Clement VII as pope, even though he was in reality an antipope. Thirteen out of sixteen cardinals questioned the validity of the election of Pope Urban due to the threat of violence from the Roman people against the Sacred College, and even Urban’s few supporters immediately retracted their election, summoning a new Conclave at Fondi which elected the antipope Clement VII. Even Saint Vincent Ferrer was convinced that Clement was the real pope, while Saint Catherine of Siena sided with Urban. If universal consensus were an indefectibly valid argument for a pope’s legitimacy, Clement would have had the right to be considered the true pope, rather than Urban. Antipope Clement was defeated by Urban VI’s army in the battle of Marino in 1379 and transferred his See to Avignon, leading to the Western Schism, which lasted thirty-nine years. Thus we see that the universal acceptance argument does not withstand the test of history.”

Robert [Clement VII] was elected pope at Fondi on 20 September 1378 by the cardinals who opposed the return of the Papacy from Avignon to Rome, and the election of Pope Urban VI in the latter town.[9] He chose the regnal name of Clement VII, and became the first of the line of ‘popes’ (now counted as antipopes) of the so-called Western Schism, the second of the two periods referred to as the Great Schism, which lasted until 1417.[10] Following a victory at Marino by Urban VI’s troops,[11] Clement, feeling vulnerable, fled Anagni to Sperlonga, then Gaeta, finally landing at Naples.[12] Received with great respect by Queen Joanna I of Naples, Clement found himself assailed by the local populace which chanted, “Viva Papa Urbano” and “Muoia l’Anticristo”.[12][13] He deemed Naples unsafe and fled by ship to Avignon, France, being greeted by five cardinals.[12]

Pope Leo XII: “15. From this it must be clearly understood that Bishops are deprived of the right and power of ruling, if they deliberately secede from Peter and his successors; because, by this secession, they are separated from the foundation on which the whole edifice must rest. They are therefore outside the edifice itself; and for this very reason they are separated from the fold, whose leader is the Chief Pastor; they are exiled from the Kingdom, the keys of which were given by Christ to Peter alone.” [Satis Cognitum]

And Siscoe/Salza are strangely quiet.

We have conservative Novus Ordites wondering whether Jorge is the pope.  Does that sound like Universal PEACEFUL Acceptance to you?  It certainly doesn't to me.

"However, I agree with Bishop Schneider that the acceptance of a Pope by the body of Bishops is sufficient to prove that the Roman Pontiff is valid. The reason I would give is that the Church is always necessarily apostolic and indefectible. So it is not possible for the body of Bishops, successors to the Apostles, to go astray following a false or invalid or heretical successor of Peter (or claimed successor of Peter). If that happened, the Church would lose Her apostolic character, which is not possible, and would lose Her indefectibility, as the visible Head of the Church, Vicar of Christ, and foundational Rock of the Church would have gone astray along with the body of successors to the other Apostles. God does not permit the gates of Hell to prevail over the Church in this or any other way."

We hare our resident Old Catholics, such as DR, trying to use UPA to justify their heretical rejection of the Church's indefectibility.