Fr. Wathen on Sedevacantism 1 - About 5 minutes long.
We are not allowed to declare that a certain incuмbent in the Chair of St. Peter is not the Pope. He may or he may not be, but we are not allowed to say it.
He also advised people not to have anything to do with SV priests especially "especially if they impose it as if it were a doctrine", i.e. the dogmatic sedevacantists.
We cannot say that he is not the pope, but evidently we can say that he "may or may not be" the pope; sounds like sede-doubtism to me. And as soon as we say that we do not know that he's pope with the certainty of faith, that doubt absolves from the obligation of submission and obedience.
They started out with this as a notion, as a speculative idea. Now it has gotten to be a doctrine.
As a "sede-doubtist", there's not much to disagree with here; my criticism of SVism is precisely with regards to the lack of authority.