How do you know? Laddy does the same thing Stubborn does: he takes a teaching and decides if it's true or false. If it's false - he rejects the teacher as false. Stubborn just rejects the teaching.
You gotta look at the big picture here, Pax. We're not just saying that this or that teaching is erroneous and therefore to be rejected. We are saying that an entire false religion has come out of Rome since Vatican II. Stubborn is basically saying that with each statement from the pope or the magisterium, one must look at it and see if it corresponds with tradition. If it does, the individual looking at it accepts it as part of the magisterium. If not, the individual rejects it as part of the magisterium. The problem here is that it's the individual making himself the pope of the pope, i.e., the individual corrects the pope as necessary. This is not correct.
Your claim that sedevacantism is basically the same has a superficial logic to it, but if you look at the big picture, it's really not the same at all. Sedevacantists say an entire false religion has come from Vatican II, and therefore the people promoting that false religion cannot be the pope and bishops, and magisterium.
The real difference between the two positions is that it's a lot easier and clearer to identify an entire false religion than to identify an error in a statement coming from a pope whom you generally believe unless he says something you disagree with. The sedevacantist rejects the person claiming to be pope in toto, so there is no need to sift his statements once he is identified as a heresiarch.
While I'm sure Stubborn would also assert an entire false religion has come out of Rome, that is not the basis on which he bases his position. He is not rejecting everything coming from Rome on that basis, but instead claiming the head of this false religion is the pope (?), and he, Stubborn, must check everything this person says to keep the good and reject the bad. Sedes don't sift anything; they throw the whole thing in the garbage.
I understand your point of view, and these are monumentally difficult questions, but I hope this helps?
Either way, you have lay Catholics rejecting a teaching that should - if the pre-V2 20th Century theologian/Laddy definition of indefectibility is true - should be free from error. Stubborn does so at least without any inconsistency; Lad rejects teachings of popes that he says can't be erroneous and which he says one can't reject.
Er, no, pre-Vatican II theologians never told us to accept any teachings from heretics.
Part of the indefectibility of the Church is not only her not teaching error but also always having an identifiable governing body. Laddy misplaced the governing body but can't let go of his indefectibility definition, which flies in the face of reality. Poor Laddy.
This is an extremely popular idea but I've never seen the proof of this claim. Can you show it to me?
When John XXXIII was elected, was he "the Magisterium"? That was 1959. What did the "motives of credibility" say, or would they say? Nothing at the time said he wasn't of "the Magisterium." Submission to his authority was required.
When Paul VI was elected, was he "the Magisterium"? That was 1963. What did the "motives of credibility" say, or would they say? Nothing at the time said he wasn't of "the Magisterium." Submission to his authority was required.
With John 23rd, that is quite plausible, but by the time Paul VI was elected, it was clear to people who knew about such things that there were serious problems in the Council that was going on at the time, in terms of its orthodoxy. Also, I think it is very likely Paul VI had a prior history of evidence of being a heretic, but I'm not knowledgeable enough to prove that.
At some point a magisterial act was weighed, or you weigh it in hindsight in rejecting either John XXXIII or Paul VI. Maybe a certain act of the Vatican II Council, maybe the promulgation or establishment of the New Mass. Point being, at some point a Magisterium that had all the marks of "credibility" - demanding submission - made a decision or act that you and other Catholics judged: a specific Magisterial act that was weighed and questioned.
Perhaps it was several magisterial acts. In any event, you and we all weighed certain magisterial acts and effectively pronounced "anti-gospel." For some that meant also therefore "not pope"; for others, simply a magisterial act not to be believed or followed.
The point being, again, for you, as well as Stubborn, I, for everyone here, some papal, magisterial act or acts - which under your standard should be accepted, believed, and obeyed - was rejected. Then, for some, the magisterium itself was rejected. But not until acts from a magisterium that had all the "motives of credibillity" violated the teachings of Scripture or Tradition.
Again, you live in a fog of "I always obey the Magisterium; it is the sole guide of truth" that is nothing more than a self-deception that, I don't know, makes you feel more Catholic, more orthodox, more traditional . . . I don't know, but your psyche needs it. But it's delusional . . .
I think the problem with your description here is that you seem to think everything was fine in Vatican II except for one little sentence or one detail that went wrong, that trads or sedevacantists or whoever you are talking about here then jumped on and started judging the pope or whatever. This is wildly inaccurate. What happened, rather, was that countless lines were crossed, which you correctly describe as heretical statements of the Council, a heretical ceremony being imposed in the place of the Mass of the ages, fake sacraments to replace the real ones, and so on and so on. There was lots and lots of proof that what was going on in Rome was not Catholic, so much proof that everyone of good will rejected the changes and novelties. We only have different ways of explaining why we reject them.