One thing I do agree with, and that's your view that some in the Resistance say that no Masses can be attended except Resistance Masses. I take issue with that as well. Though I think that those Resistance clergy who take that view are in the minority (I could be wrong about that). It's the laity attached to the Resistance who seem to more often say that no Masses can be attended except Resistance ones.
Could you be more specific -- give some concrete examples? You don't seem very sure about it.
I hate to say it, but if any clergy or laity are getting DOGMATIC about the Crisis in the Church (and the SSPX crisis is just a continuation, another battle, in the wider Crisis in the Church), then these clerics and laymen are simply wrong
There are 2 distinct realms: Ideas
(or the realm of ideas, principles) and individuals
. You can use other terms too: Abstract vs concrete, General vs specific, principle vs practice, form vs matter, etc.
In the realm of ideas
, you have to be merciless against other positions or else you aren't very serious about your
Of course I believe in the Resistance. But unless I make "Thou Shalt Attend Only Resistance Masses" as a new Commandment or Dogma of the Church, I can't condemn others, or bind their consciences. It's a prudential decision for each person. I can advise them to choose wisely; I can give them excellent reasons to go with the position I have chosen. But in the end, I can't force them. And when I fail to convince someone, I can't write them off as hell-bound.
Any Resistance-affiliated priest the least bit serious is going to promote the Resistance, saying it's the best or safest option. I do this constantly! But you can't bind this upon the conscience of others. You can't condemn others who disagree with you. You can and must part ways of course, and you can oppose any errors or foolishness. But you can't say that any specific person attending SSPX, FSSP, or even the Novus Ordo is actually on the path to Hell.