On the other hand, both Sts. Robert Bellarmine and Alphonsus Liguori are in favor of the belief that the Roman Pontiff will never defect from the faith. Likewise, all Catholic theologians seem to be agreed that "acceptatio illa Ecclesiae non est causa, sed signum et effectus infallibilis validae electionis" - that reception by the Church is not the cause, but the sign and infallible effect of a valid election (Wernz-Vidal, Ius Canonicum, t. 2 tit. 7 § 454). But the sedevacantists now inform us that the elections of Bl. John XXIII, Paul VI, JP II, and Benedict XVI were invalid due to their "heresy", despite the fact that the entire Church consented to their elections.
Likewise, sedevacantists point to, e.g., Council decrees or papal encyclicals, ignoring the fact that traditional Catholic theologians such as Billot, J.B. Franzelin, etc. hold that these are protected by at least a "prudential" infallibility which prevents them from containing heresy.
Also, sedevacantist charges that the Pope has fallen from his office are beset by the fatal flaw that they simply can't demonstrate any heresy on his part. Instead they have to appeal to imaginary teachings of the "ordinary and universal magisterium" against views that they personally don't like, or Fr. Cedaka's favorite argument based on the supposed "impiety" of the Roman Rite.
Sedevacantism is, in fact, a pathetic joke.