It is merely your opinion that sedevacantism is not consistent with Catholic teaching.
No, it is not my opinion, but it is my belief based on my readings and understanding of the teachings of the Church. But that being said, I am more than merely sympathetic with those who believe otherwise, as it is a very complex subject matter. Indeed many earlier theologians (St. Robert Bellarmine, Cajetan, John of St. Thomas, and many others), have speculated and commented on that possibility, but to the best of my knowledge, there have been no pronouncements by the Church on this important topic.
Without question, I like many other non-theologian but faithful Catholics, struggled mightily with the possibility that this pope and his recent predecessors were all heretics and, a fortiori, invalidly hold or held the Petrine Office. But to be very candid, there were a great many other post-Vatican II Catholic teachings that were brought into question for me as well, once I began to realize that there were serious problems within the Church. For this reason I do not even begin to criticize those traditional Catholics who have come to embrace Sedevacantism.
But inasmuch as I believe that the Catholic Church is the one true Church, and that Jesus Christ has promised us that He will be with us always, reasoned logic has convinced me that Jesus Christ would not allow His Church to be absent a physical head for any extended period of time. As you may be aware, the great anti-Modernist priest, Father Garrigou-Lagrange, observed that even a heretical pope can still remain as the physical head of the Church while not even being a member! This reasoning surprised me, of course, but theologians are far above my pay-grade, an especially men of his caliber. So while I don’t pretend to understand this reasoning, I have as much respect for the faithfulness and the brilliance of Father Garrigou-Lagrange as any other Catholic priest that has lived during the past 100 years.
But I guess my short answer to your very legitimate question would be that the SSPX tells me that this belief is a teaching of the Church that must be followed. And since I’ve come to reason that it is only the SSPX that is following all of the true teachings of the Church, even though some of those teachings (like the one we are discussing) are more difficult to accept than others, we must do that. If I intend to remain a Catholic for the rest of my life(which I do), I am not going to start picking and choosing some of the teachings that I might find disagreeable or less easy to comprehend.
By the way, I’m attaching an anti-Sedevacantist column of John Salza’s that was published in The Remnant last year. It’s in his typically snarky style, of course, but I’m only attaching it because he does happen to raise some valid points on this issue that are worth considering.
https://tinyurl.com/ya5k7vvf
It was nice hearing from you again.