On Protestantism: Vatican I vs Vatican II

Pius IX declared the following at the First Vatican Council (8 December 1869 – 20 October 1870):

{Vatican I, Session 2, 6 January 1870}

Likewise all other things which have been transmitted, defined and declared by the sacred canons and the ecumenical councils, especially the sacred Trent, I accept unhesitatingly and profess; in the same way whatever is to the contrary, and whatever heresies have been condemned, rejected and anathematized by the church, I too condemn, reject and anathematize.

This true catholic faith, outside of which none can be saved, which I now freely profess and truly hold, is what I shall steadfastly maintain and confess, by the help of God, in all its completeness and purity until my dying breath, and I shall do my best to ensure that all others do the same. This is what I, the same Pius, promise, vow and swear. So help me God and these holy gospels of God.

{Vatican I, Session 3, 24 April 1870}

If anyone does not receive as sacred and canonical the complete books of sacred scripture with all their parts, as the holy council of Trent listed them, or denies that they were divinely inspired: let him be anathema.

{Vatican I, Session 4, 18 July 1870}

Therefore, if anyone says that blessed Peter the apostle was not appointed by Christ the lord as prince of all the apostles and visible head of the whole church militant; or that it was a primacy of honour only and not one of true and proper jurisdiction that he directly and immediately received from our lord Jesus Christ himself: let him be anathema.

Therefore, if anyone says that it is not by the institution of Christ the lord himself (that is to say, by divine law) that blessed Peter should have perpetual successors in the primacy over the whole church; or that the Roman pontiff is not the successor of blessed Peter in this primacy: let him be anathema.

So, then, if anyone says that the Roman pontiff has merely an office of supervision and guidance, and not the full and supreme power of jurisdiction over the whole church, and this not only in matters of faith and morals, but also in those which concern the discipline and government of the church dispersed throughout the whole world; or that he has only the principal part, but not the absolute fullness, of this supreme power; or that this power of his is not ordinary and immediate both over all and each of the churches and over all and each of the pastors and faithful: let him be anathema.

Let’s proceed to what Vatican II states:

The following was declared by Pope Paul VI on 21 November 1964.

Decree on Ecumenism – Unitatis Redintegratio

The brethren divided from us also use many liturgical actions of the Christian religion. These most certainly can truly engender a life of grace in ways that vary according to the condition of each Church or Community. These liturgical actions must be regarded as capable of giving access to the community of salvation.

The term "ecumenical movement" indicates the initiatives and activities planned and undertaken, according to the various needs of the Church and as opportunities offer, to promote Christian unity. These are: first, every effort to avoid expressions, judgments and actions which do not represent the condition of our separated brethren with truth and fairness and so make mutual relations with them more difficult; then, "dialogue" between competent experts from different Churches and Communities.

Catholics must gladly acknowledge and esteem the truly Christian endowments from our common heritage which are to be found among our separated brethren.

It is allowable, indeed desirable that Catholics should join in prayer with their separated brethren.

The way and method in which the Catholic faith is expressed should never become an obstacle to dialogue with our brethren.

Our thoughts turn first to those Christians who make open confession of Jesus Christ as God and Lord and as the sole Mediator between God and men, to the glory of the one God, Father, Son and Holy Spirit. We are aware indeed that there exist considerable divergences from the doctrine of the Catholic Church concerning Christ Himself, the Word of God made flesh, the work of redemption, and consequently, concerning the mystery and ministry of the Church, and the role of Mary in the plan of salvation. But we rejoice to see that our separated brethren look to Christ as the source and center of Church unity. Their longing for union with Christ inspires them to seek an ever closer unity, and also to bear witness to their faith among the peoples of the earth.

A love and reverence of Sacred Scripture which might be described as devotion, leads our brethren to a constant meditative study of the sacred text. For the Gospel "is the power of God for salvation to every one who has faith, to the Jew first and then to the Greek".

The daily Christian life of these brethren is nourished by their faith in Christ and strengthened by the grace of Baptism and by hearing the word of God. This shows itself in their private prayer, their meditation on the Bible, in their Christian family life, and in the worship of a community gathered together to praise God.

It is the urgent wish of this Holy Council that the measures undertaken by the sons of the Catholic Church should develop in conjunction with those of our separated brethren so that no obstacle be put in the ways of divine Providence and no preconceived judgments impair the future inspirations of the Holy Spirit. 

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Very different postures on the "separated brethren". 

Was Pius IX wrong? Or was Paul VI in error? 

Aren't they part of the infallible ones when speaking ex cathedra?

Once again, Rome and its bending and syncretism to accommodate to the times.