What caused you to conclude that the popes are valid?

Well, first of all, I say that I think at one time I sort of bought into what Fr. Trosch believed concerning John Paul II, which is that he was a legal pope but not a moral one. Now, I think that it could be possible that a pope could lose his office, but I know now that can only be known surely unless it is declared de jure by cardinals during the time the Pope would be living or after his death whether he had lost his office and at which point he did. Recently, I thought about St. Peter. Did he not betray our Lord? Would that mean he lost his office then? It seems he did not. Believing heresy is of course betraying our Lord, and so if any Pope were to do that he could be held to be remaining in his office, but then again it would probably be best if he was declared to have lost it if he did indeed fall into formal heresy. The thing is that sedevacantists oversimplify or make things too clearcut concerning the papacy. Does every single Pope have to have the requirement that he be a saint in order to be validly elected or what? It would nice of course if every Pope we would have would be a saint, but history tells us otherwise. Popes have erred and have failed, even if none has actually professed any formal heresy.

How do you explain their departure from the teachings of the Church?

Well, I consider the theology and philosophy post-Pius XII popes have either for which had sympathy or believed. Many hold contradictions in their minds so easily now, and you have to understand that the common sense of the world has fooled many even though some do mean well. So many are still in the Novus Ordo, remember. A lot of that has to do with the common sense of the world infecting the minds of so many Catholics. There is the fact that even though there are naturally kind people out there, if you present the Catholic faith to one of such people and even clearly, they can be turned away. Naturalism is indeed diabolical then. Many are not of good will now sadly. Now with conservative Catholics though, you could probably get good answers to basic questions about the Catholic faith, but then they could add in things that are heretical or erroneous. Most likely, you would get similar answers if you asked Pope Benedict XVI basic questions about the Catholic faith. Obviously, there is material heresy present, but then I do not see everyone actually trying to profess any false religion entirely. Unfortunately, many end up doing so because of the contradictions with which they were fooled or raised. Of course, a sedevacantist could try to argue though that the NO is a false religion. It is but if there is someone in it who is aware of doctrinal errors running amuck, rejects all heresy, adheres to the Catholic faith, and only has what has been given to him or her, you cannot blame them being deprived of the fullness of Catholic Tradition. It does indeed start at the top. We could keep going on and on and on arguing about the sedevacantist issue, but we simply have to wait for a judgment of the Church concerning the post-Pius XII popes.

The thing is that sedevacantists oversimplify or make things too clearcut concerning the papacy. Does every single Pope have to have the requirement that he be a saint in order to be validly elected or what?

This is a nonsensical red herring, kepha, as no sedevacantist argues that one needs to be a saint to be pope.  What is required is that one possess, confess, and teach the Holy Catholic Faith.

But these dudes ARE the church!  It would take Bruce Almighty to accomplish what you are waiting for, Keph.  

The theological legalisms which Veritatis and Clodovicus put up there fit very, very well, but they don't work for me as well as a parable.  Like the janitor I mentioned earlier.  Even though he wore the uniform and pushed the cart, planting bombs either indicated he wasn't a janitor or he wasn't there in the capacity of a janitor.  Either way, as a concerned human being, you need to be evacuating the building, not waiting for his "boss" to fire him.

I am glad you say we sedes simplify things.  Through the years I have noticed that God's ways are simplicity itself---usually so simple we can't imagine "how" beforehand.  Always it is man who chooses the convoluted ways.

Oh, Keph, you are a very dear heart, but Veritatis is sooooo right.  This is immensely important.  It is every bit as important as your soul, because it is messing with your soul.  Who you follow determines where you wind up, and you have GOT to know that a servant of satan is going to lead you to hell, not heaven.  And even if you are wily enough to avoid going where he leads, there are so many who aren't.  Which is where you come in as your brother's keeper.  

First I'd have to make sure that we're all agreed that St Robert Bellarmine and Pope Paul IV lived and taught before 1900. Maybe there is a disagreement about that, the way there is about the thesis that in all his writings St Augustine never refers to a precise moment in his life.

In any case, why the reference to the year 1900 in particular?

And by the way, it is the ESSENCE of the "role" of the Supreme Shepherd on earth of Christ's flock NOT to go into error and attempt to lead the flock into it.

First I'd have to make sure that we're all agreed that St Robert Bellarmine and Pope Paul IV lived and taught before 1900. Maybe there is a disagreement about that, the way there is about the thesis that in all his writings St Augustine never refers to a precise moment in his life.

In any case, why the reference to the year 1900 in particular?

Before, I chose 1900 I think because I was considering preceeding time well before Vatican II. Plus, now I would pose the same question because I remember that gladius would give quotes of an expert (theologian or canon lawyer) or two who lived in the first half of the twentieth century. How about I alter the question though? What about before the year 1000?

EDIT: Well, Cletus, I had edited this post a few times.   I was not the most sure of why I chose the year 1900. Anyway, I think something like what I say here in response to an above quote of yours maybe would at least partly explain something of why even if not in the best way.