Here's something to grill the Sedes:
A) Why has God not intervened to strike down all these imposter popes? Why not raise up a saint and get a real pope put in place? You think God can't do this? Don't you see that He's done this in the past? He is obviously quite capable. Considering we've had apparent popes who were NOT popes (according to sedes) these past 63 years?
B) Why has God allowed us to be without a Pope for 63 years and counting?
C) Why has God not allowed the "faithful Sedes" who believe that the current Pope isn't Pope -- the TRUTH, according to sedes -- to elect a proper Pope these past 63 years?
God HAS blessed the Traditional Movement, which arose as a direct response to the Crisis. But he hasn't granted any measure of success to the sedevacantist movement. It hasn't elected a Pope, I mean -- or done anything to help solve the Crisis that "plain" Traditional Catholicism can't do.
The worst Sedes can retort is, "Your 'Pope' is a destroyer pope, tearing down the Church!" But I would respond: "You think God doesn't know that?"
It's as if God is intentionally (as in, God's will) punishing the Church with a great Crisis, and nothing mankind can do will end it.
Sedes might also retort, "Your R&R position is untenable. Just look at the recent fall of the SSPX!" But I would respond -- Sedevacantism has been a TOTAL failure since day 1. Traditional Catholicism -- starting illicit chapels, sticking to pre-Vatican II doctrine, Mass, Sacraments, devotions, books, yes -- that has borne excellent fruit, and done GREAT good to help souls keep the Faith. But sedevacantism as such? It hasn't done a single good thing for the Church, and only much harm. It still hasn't solved the Crisis, all these years. What is it supposed to be good for, exactly?
The only good part of "sedevacantism" is the part is shares in common with Traditional Catholicism in general.