7 For when this is done occasionally in the case of individuals, at great intervals of time and space, the enormity of the deed is not equally felt; but if all were suddenly to be brought together who had been baptized in course of time by the aforesaid followers of Maximianus, either under pressure of the peril of death or at their Easter solemnities, and it were told them that they must be baptized again, because what they had already received in the sacrilege of schism was null and void, they might indeed say what obstinate perseverance in their error would compel them to say, that they might hide the rigor and iciness of their hardness under any kind of false shade of consistency against the warmth of truth.
But in fact, because the party of Maximianus could not bear this, and because the very men who would have to enforce it could not endure what must needs have been done in the case of so many men at once, especially as those very men would be rebaptizing them in the party of Primianus who had already baptized them in the party of Maximianus, for these reasons their baptism was received, and the pride of the Donatists was cut short. And this course they would certainly not have chosen to adopt, had they not thought that more harm would have been done to their cause by the offense men would have taken at the repetition of the baptism, than by the reputation lost in abandoning their defense.
And this I would not say with any idea that we ought to be restrained by consideration of human feelings, if the truth compelled those who came from heretics to be baptized afresh. But because the holy Cyprian says, "that heretics might have been all the more impelled to the necessity of coming over, if only they were to be rebaptized in the Catholic Church," on this account I have wished to place on record the intensity of the repugnance to this act which is seated deeply in the heart of nearly every one—a repugnance which I can believe was inspired by God Himself, that the Church might be fortified by the instinct of repugnance against any possible arguments which the weak cannot dispel.
Source: On Baptism, Against the Donatists (New Advent)