Too bad the title of this thread doesn't actually apply to the Church Crisis since John XXIII.

The thesis of sedevacantism is that the papal claimants since John XXIII were manifest heretics before they were elected to the Seat of Peter, thereby, preventing them from actually becoming popes.

John XXIII (when he was Angelo Giuseppe Roncalli) was ipso facto excommunicated for being a freemason. Canon Law forbids Catholics as being freemasons, lest they're automatically excommunicated. No excommunicated person can become Vicar of Christ.

All of the subsequent papal claimants prior to being elected were manifest heretics.