In my experiences with various Traditional Catholics of all flavors, it's ALWAYS after someone has started to decide who is and who is not Catholic based on various narrow criteria that THEY START TO SHOW BITTER ZEAL AND GO UNSTABLE IN MANY WAYS. Fraternal charity seems to leave them. And that only seems natural, for when people begin, based on their own private judgment, to determine who's Catholic and who isn't, that's the beginning of schism, which is at its core a sin against charity. It's obvious that Lutherans, for instance, are not Catholics. But when SVs call SSPX non-Catholic or vice versa, or people call Feeneyites non-Catholic, or certain Feeneyites call those who accept BoD non-Catholic, it rots away the core fraternal charity and also demonstrate the hubris of exalting our own judgments about various THEOLOGICAL POSITIONS that aren't at the core of Catholic dogma.
Here's my rule of thumb. If you SAY THAT YOU ARE A CATHOLIC, i.e. profess Catholicism, and profess that you believe everything that the Catholic Church teaches with its supreme authority, and ... here's the key point ... if the CHURCH DOES NOT TELL ME OTHERWISE, i.e., THAT YOU ARE NOT A CATHOLIC DESPITE YOUR PROFESSION, then as far as I am concerned you ARE A CATHOLIC and I have absolutely ZERO business stating otherwise. I am not your keeper, and God is going to judge me based on whether I remained a Catholic (and other criteria) and not whether I made the correct judgment about which other people who consider themselves Catholic really aren't.
So I feel that the close and closer Father Pfeiffer gets to a schismatic home-alone red-lightism, the more he'll start to crack.