Because if sedevacantism is true, after sixty two years, there is no Church left on earth, having not only no pope, but no Bishops with authority from God through the pope. All that is left is a handful of laymen playing make believe and praying the rosary. Whenever the vocal sedes talk about how R&R would be a defection, I feel they are deaf, dumb, and blind, as if the Church for all intents and purposes ceasing to exist upon earth is not also a defection? And a greater one. For in the R&R model, faults as it may have, there is at least a Church to point to.

Well said.

Just my opinion: the sedes and their fellow travellers don't care if there's a Church, or not. The Sedes have their private faith and their soapbox, and that seems good enough for them. No Church needed.

Just my opinion: the sedes and their fellow travellers don't care if there's a Church, or not. 

It's one slander after another from you, Meg.  It's precisely because they care deeply about the Church that they have been compelled to take the position that they do.  Otherwise, if they didn't care, they'd just take the easy way out and go R&R or Motu.

During that time, it was not a question of where the true Church was any more than it was when the Roman See was vacant.

Yes, in one sense it was a question of attempting to discern where the Church was.  We had not only competing popes, but each one set up a competing hierarchy.  And of course, ubi petrus, ibi ecclesia ("where is Peter, there is the Church") turned into "Where is Peter?  Where is the Church?"

Difference there was that we did not have any of the Popes undermining the faith itself during that time.

Therefore, it's not ecuмenical.

Whether or not a Council decides to issue a solemn definition, the understanding of the Church has always been that when a moral universality of the bishops (i.e. nearly all of them) get together and teach in union with the Pope, that the teaching is protected from any substantial grave error by the Holy Spirit.

R&R completely dismiss or ignore that the Magsiterium OVERALL is guided and protected by the Holy Spirit.  That doesn't mean there can't be a slight error here or there, but nothing substantial that would ever endanger souls or the faith.

From the CE article cited earlier:

The infallibility proper to the pope is not, however, the only formal adequate ground of the council's infallibility. The Divine constitution of the Church and the promises of Divine assistance made by her Founder, guarantee her inerrancy, in matters pertaining to faith and morals, independently of the pope's infallibility: a fallible pope supporting, and supported by, a council, would still pronounce infallible decisions.

It's because of the overall "promises of Divine assitance made by her Founder" to the Church that a legitimate Ecuмenical Council is not capable of practically destroying the Church.  It's because of the indefectiblity of the Church.

Hah! That's rich. R&R will happily ignore and reject everything the Church says or does, condemn it, deride it, say it's full of heretics, ignore all the laws and rites it promulgates, but then you have the audacity to accuse others of "not needing the Church"?
Ridiculous.

THIS x1000.  R&R need "the Church" so they can put Bergoglio's picture in the vestibule and not scare away any prospective new parishioners and their contribution to collection baskets ... so they can build $50-$100 million dollar complexes.

Do you have any imprimatured work that states what you are stating....that people were wondering if they were part of the Catholic Church or not?

That's not what I'm saying at all.  They didn't know who the real pope was and to whom they had to owe obedience and whose Magisterium they would have to submit to if it were to teach.

You do realize that material error does not exclude from membership in the Church, right?

That's another reason, BTW, that R&R is much more pernicious and potentially harmful to the faith than sedevacantism.  Sedevacantists at least formally acknowledge that they have a duty to submit to Church Magisterium, whereas the R&R dispute this.  So, if they're wrong, the sedevacantists are in material error, but the R&R are in danger of formal error due to their attitudes toward Church authority.

the understanding of the Church has always been that when a moral universality of the bishops (i.e. nearly all of them) get together and teach in union with the Pope, that the teaching is protected from any substantial grave error by the Holy Spirit.

Agree, but said "teaching" has always been (in 100% of past ecuмenical councils) in the form of infallible, dogmatic decrees.  You can't imply "teaching" to V2, because it wasn't dogmatic, nor did it claim to be, nor did it "teach" anything binding.
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Your idea (as well as other's) that a non-dogmatic council is protected from the Holy Ghost is as novel as V2.  The problem lies not in you (or others); the problem lies in you projecting the same authority/protection to V2 as to Nicea.  Considering the evidence, this is ludicrous.  This is what +Vigano was saying...that V2 used the implication of an ecuмenical council (i.e. the pope with all the bishops) to trick people into accepting error when such "pastoral novelties" were not binding.  
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Satan = magic.  Magic = imaginary.  Imaginary doctrine = V2.  This is exactly what Christ warned us about:  "There will be signs and wonders..."
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R&R completely dismiss or ignore that the Magsiterium OVERALL is guided and protected by the Holy Spirit.  That doesn't mean there can't be a slight error here or there, but nothing substantial that would ever endanger souls or the faith.

The only proof you have ever provided for this is Fenton's opinion.  I consider his opinion a novelty, non-traditional and unproven.  If you can prove this, i'm all ears.
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It's because of the overall "promises of Divine assitance made by her Founder" to the Church that a legitimate Ecuмenical Council is not capable of practically destroying the Church.  It's because of the indefectiblity of the Church.

This is, again, an opinion.  Those who argue that a pope cannot fall into heresy (which is an opinion) usually also argue that the Church's indefectibility applies to fallible statements.  1) This is an opinion, which contradicts Church history.  2) This is an opinion which elevates indefectibility to a secondary infallibility, which further 3) waters down the primacy of the pope, by making his personal infallibility less relevant, because even if he's not speaking infallibly, "don't worry, the Church can't be wrong, because She's indefectible."  I don't buy it (because of Fenton pushed it in the 50s) and the idea is only recent.

That's not what I'm saying at all.  They didn't know who the real pope was and to whom they had to owe obedience and whose Magisterium they would have to submit to if it were to teach.

You do realize that material error does not exclude from membership in the Church, right?

That's another reason, BTW, that R&R is much more pernicious and potentially harmful to the faith than sedevacantism.  Sedevacantists at least formally acknowledge that they have a duty to submit to Church Magisterium, whereas the R&R dispute this.  So, if they're wrong, the sedevacantists are in material error, but the R&R are in danger of formal error due to their attitudes toward Church authority.

Excellent! Very nicely put.