First, I should add that the idea was that the majority of the bishops were right. You are right about Arianism: it flourished despite Athanasius’ efforts against it. There was a council after Nicaea (Sardica in 343, if memory serves) which validated Arianism, but it was overturned by Constantinople in 381 on the basis of not having been ecumenical.
Are you sure you meant Sardica? I don’t see anything at Sardica that validated Arianism. In fact, Sardica is a good witness for Papal Supremacy. From the Catholic Encyclopedia:
CANON III.
(Greek.)
BISHOP HOSIUS said: This also it is necessary to add,–that no bishop pass from his own province to another province in which there are bishops, unless indeed he be called by his brethren, that we seem not to close the gates of charity.
And this case likewise is to be provided for, that if in any province a bishop has some matter against his brother and fellow-bishop, neither of the two should call in as arbiters bishops from another province.
But if perchance sentence be given against a bishop in any matter and he supposes his case to be not unsound but good, in order that the question may be reopened, let us, if it seem good to your charity, honour the memory of Peter the Apostle, and let those who gave judgment write to Julius, the bishop of Rome, so that, if necessary, the case may be retried by the bishops of the neighbouring provinces and let him appoint arbiters; but if it cannot be shown that his case is of such a sort as to need a new trial, let the judgment once given not be annulled, but stand good as before.
CANON IV.
(Greek.)
BISHOP GAUDENTIUS said: If it seems good to you, it is necessary to add to this decision full of sincere charity which thou hast pronounced, that if any bishop be deposed by the sentence of these neighbouring bishops, and assert that he has fresh matter in defence, a new bishop be not settled in his see, unless the bishop of Rome judge and render a decision as to this.
CANON V.
(Greek.)
BISHOP HOSIUS said: Decreed, that if any bishop is accused, and the bishops of the same region assemble and depose him from his office, and he appealing, so to speak, takes refuge with the most blessed bishop of the Roman church, and he be willing to give him a hearing, and think it right to renew the examination of his case, let him be pleased to write to those fellow-bishops who are nearest the province that they may examine the particulars with care and accuracy and give their votes on the matter in accordance with the word of truth. And if any one require that his case be heard yet again, and at his request it seem good to move the bishop of Rome to send presbyters a latere, let it be in the power of that bishop, according as he judges it to be good and decides it to be right–that some be sent to be judges with the bishops and invested with his authority by whom they were sent. And be this also ordained. But if he think that the bishops are sufficient for the examination and decision of the matter let him do what shall seem good in his most prudent judgment.
The bishops answered: What has been said is approved.
Now as for Athanasius, were not the Eastern bishops in majority against him? Was it not the West that continually upheld his orthodoxy, amid much condemnation from the East? I just don’t see how this majority view could possibly hold water, if the majority of bishops were at one stage, Arian. Is that not a fact? I mean, I’m actually asking here - it’s not a rhetorical question.