The SSPX is part of that Church, and so it's the work of God.
Our Lord said to judge a tree by its fruits. The fruits of the SSPX have been salvation for many souls, vocations, sanctity of life, more Catholics living their Catholic Faith during the week, and many conversions. The majority of evidence points to the SSPX being "of God".
And the SSPX defended the Faith on a global scale, with chapels, seminaries, and priests all over the world. They had 500+ priests at their peak. The SSPX dwarfs any sedevacantist group in terms of priests, chapels, parishioners, or any other metric. So Catholics of good will have voted with their feet who they think is safer or more Catholic.
The SSPX has become the neo-SSPX now, and is collapsing before us. But at the same time, the true SSPX continues on in the form of the Resistance.
So when I promote the "SSPX" I mean the SSPX before 2011 -- and after 2011, the Resistance.
Sure, with human beings there are always bad apples. But you could say the same thing about the Catholic Church in general! There are always some bad fish caught in the net.
Sedevacantism, on the other hand, is simplistic, defeatist, and most Catholics (even good-willed Traditional ones) reject it. Many of them flirt/flirted with Sedevacantism, but they usually give it up and talk about it like a temptation or sin they fell into.
How many good Traditional Catholic forums forbid Sedevacantists to participate, because of the noxiousness of their presence (with a few notable exceptions)? They only like to argue about the Pope question. They refuse to believe in any element of mystery in the Crisis in the Church. They want to understand it all with their puny, poorly educated human minds. Some of them have only been Traditional for a few years, or even a few months! And yet they'll happily throw the wisdom of wise priests and bishops right into the trash can.
Again, I'll admit that it doesn't apply to *every* Sedevacantist, but it applies to far too many of them.
After all, once you add "sedevacantist" to your name, you have to defend that difference by being obsessed with the issue. If your daily life or discourse were the same as a regular Traditional Catholic, then why the extra adjective "sedevacantist"?
That adjective stares at you in the mirror every day, imploring you to do something "different" than your fellow Traditional Catholics who aren't "sedevacantist". And far too many sedevacantists heed the call.
Their "universal unwelcomness" forces to mind the fate of the cursed Jews, forced to wander the earth without a home, since they rejected the Messiah they had been formed by God for centuries to recognize and accept. The Jews had been blessed so much, so highly favored, and they returned the favor by crucifying the Just One.
Sure, Our Lord said His followers would be hated.
But the Jews were also universally hated throughout Christendom during the Middle Ages. They were a persecuted people.
So which kind of persecution/unpopularity are the sedevacantists enduring today? The persecution endured by the just man, or the persecution endured by the wicked?
The world hates Bishop Williamson (the Just) but it also hates Charles Manson and Jeffrey Dahmer (the wicked).
So simply being "hated by the world" proves nothing about a person or group.