As you can read, this was posted during the pontificate of Pope Benedict, and in happier days in the SSPX:

SUPLEMENT

No. 3

THE SEDEVACANTISM


The question of sedevacantism was raised by many, and Archbishop Lefebvre himself wondered how it was possible for a Pope to preside over the destruction of the Church. For, in short, a serious problem is imposed on the conscience and faith of all Catholics since the pontificate of Paul VI, Archbishop Lefebvre said in an interview with the Figaro newspaper in August 1976. How can a Pope, the true successor of Peter, who is not lacking in the assistance of the Holy Spirit, preside over the destruction of the Church, the deepest and most extensive of all its history, in such a short space of time, something that no heresiarch has ever been able to do? (1) “Do we really have a Pope or an intruder sitting on the throne of Peter? Blessed are those who have lived and died without having to formulate such a question.” (2)

But Archbishop Lefebvre did not leave this question unanswered. Even if this question cannot be fully clarified, or rather, for this reason, because there is no infallible teaching of the Magisterium in this regard, a reserved attitude is imposed. “Apart from the occasions when he uses his charism of infallibility, the Pope can err. Why then is one scandalized and says, ‘So he is not Pope,’ as Arius who was scandalized about the Lord’s humiliations when he said in his Passion, ‘My God, why have you forsaken me?’ and Arius concluded: ‘So he is not God!’ We do not know how far a Pope led by I do not know what spirit or formation, subjected to I know not what pressures or through negligence, can drag the Church to lose the Faith, but we see the facts. I prefer to start from this principle: we must defend our Faith; this is our duty. In this regard there is not the slightest doubt.” (3)

More clearly, Archbishop Lefebvre wondered: can the formal heresy of the Pope be affirmed? Who has the authority to declare this? Who will make the admonitions provided for by Canon Law, necessary for this finding? Moreover, if the Pope is not Pope, in what situation is the Church? Who will show us the future Pope? How can he be designated if there are no more cardinals, since the current Pope is not Pope and therefore cannot validly create new cardinals? And Archbishop Lefebvre concludes: “This sedevacantist spirit is a schismatic spirit.” The visibility of the Church is too necessary for her existence for God to omit it for decades. (4)

For these reasons, Archbishop Lefebvre said to his priests and seminarians: “I cannot admit that, within the Fraternity, someone refuses to pray for the Holy Father and therefore refuses to recognize that there is a Pope. It would be to enter on a path that is a dead end. I do not want to lead you to a impasse, to put you in an impossible situation.” (5)

But then why in the diocese of Campos do some accuse or suspect the priests of the Society of St. Pius X of being sedevacantists? The answer; as curious as it may seem, is this: those who accuse the priests of the Society of St. Pius X of being sedevacantists reason in the same way as the sedevacantists themselves. For them; either the Pope is Pope, and then everything he says is right and has to be heeded, or else, if he teaches serious mistakes, he is not Pope. The truth is that this dilemma is a false dilemma. The truth is that the Pope, even though he is Pope, can err. Apart from cases where the Pope engages his infallibility, he can err. Today we see the Pope err and spread the error and even heresies. To denounce it is not a sign of sedevacantism, but of Catholicism. In addition, all the priests of the Society of St. Pius X sign a docuмent, before their ordination, saying that they recognize Benedict XVI as Pope and that they will publicly pray for him. Therefore those who attack the Fraternity because of this do not know what they say.

As for those who defend sedevacantism, we have some advice to give. A counsel of prudence and humility. If the Holy Church has not defined the conditions in which a Pope ceases to be Pope, it is appropriate not to advance on this ground, because this would also be to love novelties, and to abandon the sure paths of doctrine already defined. To love the Tradition of the Church is precisely to reject novelties and to stand on the firm ground of the teaching of the infallible magisterium of the Holy Church. One must also take into account the proper character of modernism and liberalism, which admit a multitude of hues and degrees. Moreover, the heresies of the reigning Pope are not necessarily formal heresies; but they can be only material, as in the case of those who have no notion of going against the magisterium of the Church. Then, even in the case of formal heresy, the question remains as to whether the Pope loses his pontificate in this case and how. All this invites us to sobriety, and the example of Archbishop Lefebvre and Bishop Antonio de Castro Mayer should be sufficient to preserve us from this conclusion, which sins by excess by wanting to give, not to say impose, a definitive solution to an issue for which the Holy Church has not yet provided a solution.

The danger of schism is certain for those who follow the sedevacantist doctrines. Experience shows that this is not just a hypothesis. There are already several Popes elected by the sedevacantists. More than ten, it seems. This should be enough to inspire greater sobriety in the defenders of a position that leads to such follies, endangering the eternal salvation of their souls, and many others.

1- Mgr. Tissier de Mallerais – Marcel lefebvre, éditions Clovis, p. 515

Ibid. – p. 533

Ibidin – p. 534

4- Ibid., p. 536

5- Ibid. – p.g. 536

What have the modernist given up?  Everything "they" do and say against church teaching has already been condemned.  Do you send your children to public schools and let them  indoctrinate them? 
Pope Pius X must have been an extremist for saying the modernists should be beaten with fists!
I can see the direction will be to share altars with the modernist like the Gernans do in the "mixed" Catholic/Lutheran regions.  To live in peace.  Sounds like the spirit of assisi.
It would be better if you held the "wait and see" position,  to stay silent and have nothing to do with the novus ordo.
The spirit of compromise has already signaled defeat.

Good points!

Garbage.  You cannot affirm a Catholic Church that, as +Lefebvre stated, 1) lacks the Marks of the Catholic Church, 2) a Catholic Church that has corrupt Modernist Magisterium, and 3) a Catholic Church that has promulgated, implemented, and imposed a Protestantized bastard Rite of Mass. 4) Those of you who continue to affirm this are nothing more than thinly-veiled Old Catholics (with a couple of minor distinctions).  This has precious little to do, fundamentally, with the "5 Opinions" question, that indeed has not been settled.

1) The conciliar church is not the Catholic Church.
2) The Church's Magisterium can never be corrupted - reference your own post for this. All you need to do is believe the quotes in your own post.
3) The pope (Paul VI), is the one who imposed the NOM, not the Catholic Church.
4) If anyone, you are the one affirming this. Therefore, if anyone, you are the Old Catholic.

What has been settled by both Vatican I and perennial papal Magisterium is that the See of Peter cannot be blemished by error, and the Council of Trent anathematized those who would hold that the Rite of Mass used by the Church can be an inducement to impiety.

Again, the conciliar church is not the Catholic Church, and the Rite of Mass used by the Roman Church is the Mass of Pope St. Pius V - which is the Mass Trent decreed it's condemnation of to all who said *that* Mass was an inducement to impiety. 

V1 was all about papal infallibility, both the perennial magisterium and V1 teach that the see of Peter cannot have any blemish *when the pope speaks ex cathedra,* which is as +ABL said above but you call "Garbage:" "The truth is that the Pope, even though he is Pope, can err. Apart from cases where the Pope engages his infallibility, he can err."

If I wanted some good that you possessed and the only way I could obtain it was by physically putting my hands around your neck, but I never went through with it.  I only thought about it and maybe told my close friends.  Different punishment than actually committing murder.
The men teaching the church errors are acting on ideas that are condemned by Holy Mother Church.
That means the church never had the right to defend or condemn false brethren. 
Wait and see folks should pray more and argue less, but support Catholics that ultimately support you. 

I agree, but the when She condemns heresies and errors she is infallible. Heresies and errors are sins. Sins pertain to morals. When she says something is a sin, she is infallible. "If anyone saith "___________" let him be anathema" is infallible because it always concerns morals.

You must understand the safest path as far as pre Vatican II sacraments and judgments.  I assume we are taking over each other on these issues but agree on fundamentals but disagree on applications in some areas.

Far as I'm concerned, V2 and the NO religion is from hell.