The case of Liberius.
The matter is historically very difficult to determine definitely in all its details. However, Pope Liberius (p. 352-366) excommunicated Saint Athanasius. He wrote about this excommunication proudly to many persons.
Initially, Liberius stood behind Athanasius. He stood behind Nicaea. He bravely went up to Milan to meet the Emperor, who was espousing so-called “semi-Arianism.” Semi-Arianism was a muted form of Arianism. It was supposed to be a “compromise” kind of doctrine.
The semi-Arians saw themselves as those who promote “peace” and “tolerance” within the Church and the Empire. Since the Arian controversy was raging and rending the whole world, ecclesiastical and political, in two, unity was highly desirable. If the pure Arians outright said that the Son is totally other than the Father, of a substance unlike the Father, the semi-Arians said that he was “similar” to the Father.
Well, Liberius went up to Milan to face the Emperor. Bravely he stood his ground, and unjustly was he sent into exile. After some years in exile, however, he pined away and regretted his misery. Soon the semi-Arians heard of this. And they got him to agree to excommunicate Athanasius.
Then, the got him to sign a semi-Arian creed. The emperor and the ecclesiastical semi-Arians had arranged, before this time, numerous synods and gatherings of bishops that destroyed or undermined the faith. So, there were many heretical or heterodox documents floating around.
Everyone was very confused as to what the faith was.
Although on the books was the Great Ecumenical Council of Nicaea, already ratified. If the people at that time wanted to avoid confusion, they needed only plug their ears to the latest synodal document, plug their ears to the latest finding of this gathering of bishops or that, and study the truly infallible teaching of Nicaea, and they would have kept their course soundly. Some did. Some didn’t. But that would have been their compass in those troubled seas.
Well, just what semi-Arian document did Liberius sign? The absolutely certain answer to that question might not be known until the Eschaton.
However, the scholars of the Denzinger text indicate that it was the one in which we find the following propositions. 1) The Son should not be confused with the ‘unbegotten God’. A very nifty proposition for wafflers! Why? Because the property ‘unbegotten’ is obviously opposed to ‘being a Son’. The Son is begotten. But the creed conflates ‘being true God’ with ‘being the unbegotten God’. Thus, without expressly denying that the Son is “true God” the creed implicitly denies it. It certainly does not affirm it. (Although Nicaea did affirm it! Thus, once again, if the people of the day had stuck to the real fullness of the truth, and not let later watered down texts lead them astray, they would not have been fooled by a merely ‘half truth’.)
But the creed gets worse. It also states, “We do not place the Son in the same order as the Father, but we say that he is subject to the Father.” This text is very difficult to spin in a positive direction. On the surface, it seems to rank the Son as “not true God”. He is “subject” to the Father, etc.
Thus, this semi-Arian creed combines the following: a) watered down expressions of the true faith (half truths); b) implicit denials of elements of the true faith; and c) apparently, explicit denials of the true faith. In short, a very bad thing.
Yet, Pope Liberius signed off on it. Not a few very respectable Catholic scholars (Newman, Petavius, et alia), who profess the Faith of Vatican I, see Liberius here as having caved to the Arian error.
Some try to argue that he signed the Creed against his will and at the force of arms. That is a stretch. He was under duress. But he willingly signed. In fact, the Church’s Magisterium teaches that there is a difference between duress and absolute constraint, between “forced” and “forced”. If you, because of fear, you actually submit to being baptized, you are validly baptized! But if you in your heart refuse the baptism and they drag you, you are invalidly baptized. Thus, doing something because of fear does not mean you do it without freedom.
Apply that mutatis mutandis here. Pope Liberius was afraid and fearful, but he actually consented.
Some try to argue that the creed was ambiguous and so not overtly heretical. Perhaps.
But he certainly let down the Holy Apostolic Catholic and Roman Church at a time of great crisis, in which political factions desired some middle between orthodoxy and total depravity. The compromise path labeled the depravity what it is, depravity, but pitted it against the true orthodox faith as against something too rigorous, something “inflexible” (Newman, Arians of the Fourth Century, Longmans 1897), p. 322.
Obviously, the “middle path” the Emperor and the semi-Arians carved was a false path; they identified the extremes badly. The true faith is never to be considered “inflexible” (as a pejorative). It is the only truth there is known to man in matters supernatural! And without it, one cannot have charity towards the neighbor whom one should love for the greater love of God.