For this reason it has always been necessary for every Church--that is to say the faithful throughout the world--to be in agreement with the Roman Church because of its more effective leadership.
Agreement over matters of what? Oh, wait, don't answer that - it might make it conditional and ruin your whole argument.
I asked if you have an example of an instance where you refuted the heresy of the sppx re. the Dogmatic Teachings of Vatican I. Are you searching for one?
"Remember that if you cannot get to a true (sic) Catholic Mass celebrated by a good (sic) traditional priest, you should not attend the New Mass or the Indult Mass, and this even if it is the only traditional Mass available".
For example, the Society, presumes to set itself up as what many consider a virtual counter-church & magisterium: in addition to employing private judgment to determine what is and what is not Catholic, the Society presumes the competence to annull marriages without the permission of the Pope and bishops, it confirms Catholic young people without permission, and alleges that the sacraments of the Roman Catholic Church are invalid or dangerously dubious. It also reportedly brings in much revenue by exploiting every real or imagined problem in the Church to its own advantage. The Society has also reportedly unilaterally imposed censures on lay persons and attempted to defame those priests who have left their ranks.
It's founder appears to have done just that:
"I entered these negotiations because Rome's reactions in the second half of last year had raised in me a faint hope that these churchmen had changed. They have not changed, except for the worse. Look at Casaroli in Moscow! They have spiritual AIDS, they have no grace, their immunity defense system is gone. I do not think one can say that Rome has not lost the Faith. As for an eventual excommunication, its disagreeableness diminishes with time." (Private talks quoted in Williamson's Letter from Winona, Aug. 1, 1988).
*I'm sure you'll agree with me that Lefebvre was voicing a heresy and declaring Rome had lost the Faith in contradiction to the Dogmatic Teaching of Vatican I.