768 28. If the pope with a great part of the Church thought so and so, he would not err; still it is not a sin or heresy to think the contrary, especially in a matter not necessary for salvation, until one alternative is condemned and another approved by a general Council. Condemned. This is I think out of all the given quotes, is the most damning. For this is the root tenet of the resistance position to lawful authority, and the Roman Pontiff. It looks like if this was word for word, a +Williamson comment.
Lethal!
This one is directly lethal to the SSPX's
modus operandi:
Council of Constance, 1414-1418 209
17. Priests of Christ, living according to His law and having a knowl- 643
edge of Scripture and a desire to instruct the people, ought to preach
without the impediment of a pretended excommunication. But if the
pope or some other prelate orders a priest so disposed not to preach, the
subject is not obliged to obey. Condemned