Prior to Vatican II certainly, and for the most part prior to Pope Francis, conservatives held that Papal Canonizations are infallible. And this is considered to be the majority opinion of theologians by the CCS:

The Congregation for the Causes of the Saints: “it is the opinion of the majority of theologians that canonizations done by the Holy Father enter within the limits of his infallible teaching authority.” [2006, letter to the author]

So what happened? All of a sudden, during the reign of Pope Francis, a series of articles by traditionalists and conservatives argued vehemently that canonizations are not infallible. The explanation is obvious. The opponents of Francis and of Vatican II do not wish to accept that John 23 and Paul 6 and even JP2 are Saints. That would make it very difficult to claim, as so many of the accusers of Pope Francis have said, that JP2 committed idolatry at Assisi (and if he did not, then neither did Francis). It makes it very difficult for them to accuse Vatican II of heresy, since the Council was of John 23 and Paul 6 and was replied upon for many of the teachings of JP2 and of the Catechism published by his authority.

The reason for this change of position by conservatives is that they do not wish to accept the teachings of the recent Pope Saint and the recent Council. But they cannot accuse Saints of being part of the alleged “infiltration” of the Church by an evil conspiracy, so they first deny that they are Saints.

But if J23, P6, and JP2 are not Saints, then perhaps Popes Pius V and Pius X are not Saints, that is, IF their claims about papal canonizations are applied consistently. You cannot claim that some papal canonizations are infallible and others are not — based on your personal evaluation or that of the subculture which you follow. That would make you yourself the infallible canonizer, not the Pope.

One of the reasons given for acceptance of the TLM is that it came from Pope Saints Gregory I, Pius V, and Pius X. Another reason is that the Saints supposedly drew their spirituality and holiness from that Mass. (That last point that the make is idolatry, since they are attributing the holiness of the Saints, not to worship, prayer, adoration, Scripture, and the Eucharist, but to non-essential points of exterior liturgical form.) If all those Saints are perhaps not Saints, then they undermine their own position with such a claim.

So it is intellectual dishonest for them to claim that canonizations are not infallible, merely because it strengthens their gravely immoral faithless accusations against the recent Pope Saints and the recent Council.

And now I must also point out that even if a Pope is like Alexander VI, clearly not a Saint, his teachings are of Christ and the Holy Spirit; his faith is never failing; and the Apostolic See is unblemished by any grave error.

They think to strengthen their accusations against Popes by casting doubt on their sanctity. But in the end their accusations are really against Christ himself.

Unam Sanctam: “But this authority, even though it may be given to a man, and may be exercised by a man, is not human, but rather divine power, having been given by the divine mouth of Christ to Peter, and to him as well as to his successors, by Christ Himself, that is, to him whom He had disclosed to be the firm rock, just as the Lord said to Peter himself: “Whatever you shall bind,” [Matthew 16:19] etc. Therefore, whoever resists this authority, such as it has been ordained by God, resists the ordination of God. [Romans 13:2]”

When the Pope declares a previous Pope to be a Saint, especially in that case though not only in that case, he exercises divine authority from Christ. Even if it were possible for such a canonization of a past Roman Pontiff to be in error, such that the past Pope were not as holy as he was thought to be, the exercise of the Keys by any Roman Pontiff are free from grave errors on both doctrine and discipline. And so the argument that says the recent Pope Saints were not really Saints, therefore, listen to these accusations that they erred gravely, is itself an argument contrary to dogma and therefore heretical.

80. “Wherefore, let the faithful also be on their guard against the overrated independence of private judgment and that false autonomy of human reason. For it is quite foreign to everyone bearing the name of a Christian to trust his own mental powers with such pride as to agree only with those things which he can examine from their inner nature, and to imagine that the Church, sent by God to teach and guide all nations, is not conversant with present affairs and circumstances; or even that they must obey only in those matters which she has decreed by solemn definition as though her other decisions might be presumed to be false or putting forward insufficient motive for truth and honesty. Quite to the contrary, a characteristic of all true followers of Christ, lettered or unlettered, is to suffer themselves to be guided and led in all things that touch upon faith or morals by the Holy Church of God through its Supreme Pastor the Roman Pontiff, who is himself guided by Jesus Christ Our Lord.”
[Pope Pius XI, Casti Connubii, 104.]

Ronald L. Conte Jr.