Sneaky keeps attacking me as if I were an R&Rer. I am not. I agree that most of the sedevacantist arguments against R&R are quite valid. I am of the opinion that the Holy See is most likely vacant at this time.
But here's the catch. It's a very crucial distinction. You might argue that it's semantics, but it's not. It makes all the difference in the world.
I adopt a posture of humility. I concede that I might be wrong about this, admit that I arrived at my conclusions based on my private judgment, and defer to the judgment of the Holy Catholic Church on the subject, because only the Catholic Church can decide who is pope and who is not. This makes all the difference in the world because Catholics CANNOT go around determining papal legitimacy based on private judgment. Papal legitimacy is something that must be known with the certainty of faith, and that can NEVER happen when it's rooted in private judgment. In my Pius IX infallibility example, the logical conclusion of sedevacantism proper is to say that it's OK to Pope-Sift, i.e. to reject the teaching of a Pius IX due to allegations of illegitimacy. No, the legitimacy must be known with the certainty of faith a priori to the dogmatic definition. Based on that certainty of faith, then, I must accept the dogmatic teaching regarding papal infallibility and change my mind on the subject. There were several catechisms out there before Vatican I that rejected the idea of papal infallibility. After Vatican I, however, these were all changed and a lot of critics of the idea humbly accepted the teaching of the Church. Then there were the Old Catholics, who considered papal infallibility to be a heretical novelty. Sedevacantism would vindicate their stance.
That's where Bishop Sanborn gets it completely wrong in his condemnation of "opinionism". He doesn't realize that there can be certainty and then there can be certainty, meaning that one can have a certainty that's arrived through the natural intellect and one can have the certainty of faith, and that these are two different certainties.