"I'm struggling though in understanding how all the post VII Popes are not also antipopes. Most especially JPII for his Koran kissing, Assisi... help me to understand how the Sedevacantist are not correct"
Vatican I clearly teaches that popes will reign perpetually against Sedevacantism:
"[T]he true doctrine concerning the establishment, the perpetuity, and the nature of the apostolic primacy. In this primacy, all the efficacy and all the strength of the Church are placed. (Vatican I, Pastor Aeternus, chapter 1)" (UnamSanctumCatholicm.com, "False Principles of Sedevantism (Part 1)).
Br. Alexis Bugnolo explains some other problems with Sedevacantism:
Sedevacantists hold in general that there have been no true popes since Pius XII. They accept the error of Luther that there is no authority or unity in the Church except that which is given the individual by the virtue of Faith. Thus, holding themselves as purer than all others, after the manner of Jansenists, they judge nearly everyone a heretic and thus outside of the Church. Their special target is all who hold an office which comes down through Apostolic Succession, because that is the real threat to their error and their egos." [https://fromrome.info/2020/01/19/flagship-of-sedes-presages-ppbxvi-movement-victory-in-2020/] - Fred Martinez
One of the great Catholic Monitor commenters, Debbie, said the following to me and the knowledgeable commenter Aqua:
"Fred and Aqua. I'm struggling though in understanding how all the post VII Popes are not also antipopes. Most especially JPII for his Koran kissing, Assisi, changes to the catechism. Please help me to understand how the sedevacantist are not correct."
Here is our response: