Can you explain sede doubtism?
It's basically a middle road. I agree that individual Catholics cannot go around deposing Popes, but I also agree with the sedevacantists that if they are certainly Popes then we owe them our submission. But I consider their status to be objectively doubtful. Consequently, we can reject their teachings and their authority without schism. I can go into more details, but that's it in a nutshell. You see, normally we accept Popes with the certainty of faith. If we do not have that certainty of faith regarding their legitimacy, we are NOT IN FACT SEDEPLENISTS in the true sense, but rather what I have called (partly tongue-in-cheek) sede-doubtists. And both +Lefebvre and +Williamson and +Tissier have expressed doubts (or at least lack of 100% certainty of faith). Consequently they do not hold them legitimate with the requisite certainty of faith and are not therefore true sedeplenists.