His position is less extreme than the one taken by Archbishop Lefebvre, Bishop Williamson, and just about every priest alive(including the SSPX priests you accept communion from). Go condemn them instead of crusading against some layman for following them.
I hold the same view Archbishop Lefebvre did, not really a less extreme one. All that being said, if a Pope ever clearly in the future declares ex cathedra, or holds a dogmatic ecumenical council to declare, that there is no salvation without becoming a formal and visible member of the Catholic Church, I would certainly submit to it. But the bottom line is, if Florence was itself clear on this matter (remember Florence uses the word "outside" which is less specific than "formal and visible member") well then clearly all the Trad clergy missed the memo. I doubt this. Seems a lot more likely to me that just Florence/Unam Sanctum/whichever old documents aren't as clear as Last Tradhican thinks they are.
And if I'm really a "new convert who doesn't know anything about Catholicism" (OK maybe) then why in the world should I listen to randoms on Cathinfo over basically every priest in the world, whether Traditionalist or not? (they all disagree with the Feeneyites here.)
Now, personally, if somebody wants to disagree with Archbishop Lefebvre, Bishop Williamson, and "just about every priest alive" and agree with Fr. Feeney instead, perhaps one can do that in good faith. I'm certainly not going to run around calling those people heretics, because it seems fruitless to me (bigger fish to fry and all that.) My even bigger issue with the Dimonds isn't so much that they take those positions themselves, but that they also act as though they have the authority to condemn other Catholics for disagreeing with their interpretation of EENS. That's the *core* issue IMO