In my own mind, this has crossed a line. Clearly not everything ever taught by any Pope ever is infallible. Unfortunately, many sedevacantists exaggerate the scope of infallibility ... as an overreaction against R&R. But I think we've crossed a line from the mere technicalities of infallibility into what I would consider to be a defection of the Magisterium and Universal Discipline. I subscribe to Monsignor Fenton's line of thought on this matter.
This is my understanding of the Holy Catholic Church as well. With Vatican II and the New Mass, we are not talking about an isolated passing thought in some Encyclical. What we have here is a new theological system. Along with it has come a Mass that has done grave violence to the Church's revered Liturgical Tradition. My faith in the holiness and the indefectibility of the Church rule out this possibility as a matter of faith. I believe this with the certainty of faith.
See, a material continuity of the Church does not suffice for indefectibility. If the Church can by her official teaching and discipline bring grave harm to souls, where we feel that we cannot in good conscience participate in whatever this is, then the Church would have defected in her mission. At that point, what good would a mere material continuity be. In that case, souls would be better off if such an institution were in fact to go extinct. It's one of the main reasons Our Lord left the Church with teaching authority, so that the sheep in heeding it would be kept from going astray.
If I were to tell St. Robert Bellarmine that I considered it a possibility that the Church could hold an Ecuмenical Council that endangered the faith and a Roman Rite Mass that harmed souls, he would unquestionably without the slightest hesitation declare me a heretic and outside the Church.
I suppose I don't understand why I'm obliged to believe this with the certainty of faith. And either way the pickle seems to be basically the same. In neither case do I see why Mssgr. Fenton's reasoning is infallible.
If you instead told St Robert Bellarmine that you considered it a possibility that an antipope could take over Rome, convince 99% of people who profess the Catholic faith that he was Pope, all the while there is no real pope at all, hold an "Ecuмenical Council" but a false one, and do all those same things, but REALLY there'd be no true pope at all, and only a tiny number of bishops and priests (not even any cardinals) realizing the real truth of the matter, what do you think he'd say about you then?
I could be wrong, I'm no expert, but i suspect he'd call you a heretic. Admittedly, I'm not sure St Cyprian would call you a heretic in either case.
Mind you, I normally agree obviously that we shouldn't sift Popes like this. And if its true that past encyclicals cannot err on "big issues" like Church and State, etc. than clearly there's a big, big problem right now.
Honestly, maybe I'm guilty of error, but I'm not convinced of any of this stuff. I definitely think its a real possibility that we need to be more minimal about what we can know for certain than theologians thought in the past. I really hope one way or another a future Trad pope can clear things up for us, either how we can know something is really universal ordinary magisterium (if R + R is correct), or how we can know someone is really Pope (if SV is right)