Because it is not following Catholic principles. A theological opinion, perhaps.

prin·ci·ple
noun

• 1.
  a fundamental truth or proposition that serves as the foundation for a system of belief or behavior or for a chain of reasoning

Francis is a heretic.  Heretics are barred from the papacy.  You may disagree that Francis isn't a heretic, and that could be an opinion, but to say it doesn't follow principles?  Yawn...

You defined principle. You needed to define opinion. If we all stuck to certain Catholic principles we would not be in this mess.

Because it is not following Catholic principles. A theological opinion, perhaps.

A theological opinion is PRECISELY based on catholic principles.    Doesn't mean the opinion is always correct, but it does have a foundation in catholic principles.

Au contraire mon frère.  We are in this mess precisely because the man you call pope is actively engaged in trying to destroy any and all Catholic principles over in 'the Conciliar Church'.  I'd much rather attend the local Nervous Ordo but that is impossible for numerous reasons.

Are you attending your local Nervous Ordo?  Why or why not?

Yes, you are referring to the larger mess! No I don't attend the NOM, I'm a Traditional Catholic. I refer you to chapters 3 and 4 of Open Letter to Confused Catholics: http://sspxasia.com/Docuмents/Archbishop-Lefebvre/OpenLetterToConfusedCatholics/Chapter-3.htm
You would rather attend the NOM???

After the split of the nine Archbishop Lefebvre ordered that the 1962 rubrics would be used in the seminaries. He never demanded this in the priories and chapels. He himself in his private Masses said in Our Lady's chapel in Econe used the older missal and rubrics. In fact he never seriously learned the 1962 rubrics.

Archbishop Lefebvre's conferences to the seminarians at Ridgefield 1982/83:
https://ia802702.us.archive.org/18/items/LefebvreRidgefield8283A/Lefebvre%20Ridgefield%2082%2083%20a_text.pdf

Excerpt:
"Well, this liturgy (of John XXIII) is the liturgy of Econe. It is the liturgy
I myself have been using now for 20 years. It is a liturgy we use,
more or less, everywhere in the Fraternity,"
"But this fact, this refusal of Fr. Zapp's was an unveiling of
another thing more important..."

Because it is not following Catholic principles. A theological opinion, perhaps.

Give us a break.  Refusing communion with and submission to the hierarchy, to the Magisterium, is contrary to every known Catholic principle.  To claim that the Catholic Church has become corrupt in its Magisterium and in the Mass is contrary to every known Catholic principle.  No Catholic theologian has ever asserted that it's possible for the Church to become corrupt in its Magisterium and in its Public Worship.  Those are the "principles" of Old Catholicism, Eastern Orthodoxy, and Protestantism.  Your babbling about Catholic "principles" borders on the absurd.

We have walls of papal teaching (that have been posted repeatedly here) that the Magisterium can never be blemished by error.

Dogmatic teaching of Vatican I, Pastor Aeternus:

Indeed, their apostolic teaching was embraced by all the venerable fathers and reverenced and followed by all the holy orthodox doctors, for they knew very well that this See of St. Peter always remains unblemished by any error, in accordance with the divine promise of our Lord and Savior to the prince of his disciples: "I have prayed for you that your faith may not fail; and when you have turned again, strengthen your brethren."

If Vatican II and the post-Vatican II "Magisterium" does not constitute (according to R&R) the See of Peter being "...blemished by error," then there's no such thing and the words above are meaningless drivel.  And they are, according to R&R.

What's more, the Council of Trent anathematized the proposition that the rites used by the Church can be an inducement to impiety.

Many of you are treading on dangerous ground, flirting with heresy, and have essentially become thinly-veiled Old Catholics.

And, of course, Plenus here keeps dishonestly conflating the issues that The Nine had with "sedevacantism," even though not all of The Nine were actually sedevacantists, and it was not one of the key issues for The Nine.  What were at issue are some of the very same principles that The Resistance criticize neo-SSPX for.

Yes, except he isn't the only one. The change occurred a few pages back.

Yes, that shift has occurred numerous times during this thread, and I try to call it out each time I see it.  It's simply dishonest.

Not to mention that it serves the purpose of diverting attention away from the real issues raised by the Nine.