For although Liberius was not a heretic, nevertheless he was considered one, on account of the peace he made with the Arians, and by that presumption the pontificate could rightly be taken from him: for men are not bound, or able to read hearts; but when they see that someone is a heretic by his external works, they judge him to be a heretic pure and simple, and condemn him as a heretic.
Great quote.
Puts all the moaning about not being able to say the V2 popes were "formal" heretics in perspective: a convenient evasion of the head(s) of the roaming monstrum.
Not to really add anything, but just to confirm:
Your quotes above of Gerard van Noort and Joaquín Salaverri S.J., theologians of the 20st century, show that they basically agree with St Robert. Both call it the more common opinion, and van Noort explains how theological reasoning for this opinion is strong.
Still the whole "Trad-world" is full of know-it-alls, who try to impede people to do the obvious: E.g.: Treat anyone attending or agreeing with or not rejecting those pagan Assisi events as a manifest heretic and outside of the Church. (just to name one example, same thing with V2, bastard mass, and much more)
Pax Vobis and Ladislaus: could you please quote any kind of authority authorizing you to run around and proclaiming that its not ok to call manifest heretics what they are? You've posted rivers of alphabetic characters, but you've failed to substantiate your ideas with evidence, no quote of a Saint, a Father, a theologian, at all.