Although we clearly do not wish either to be or to appear liberal, it behooves us to be honest with the faithful about these days' obligations just as we are about the penitential obligations: only the power of the keys can determine our concrete obligations, as Catholics, on any given day.
While we must urge and exhort the faithful to keep the traditional days of feast or of fast, it needs to be clear that they are not obliged under pain of sin to do so when the power of the keys has eliminated the obligation. Unfortunately, the faithful are sometimes convinced of an obligation that does not exist and then violate that "obligation" culpably. The sin is real in that case, despite the fact that the obligation is not. Let us not be the cause of such sins by being unclear or culpably wrong about these points ourselves in our communications with the faithful.
This is very important, it's about the proper formation of consciences. The SSPX will do more damage than good if they are improperly forming consciences. Let those who would do more, do more. But at least clear up unnecessary sins for the others.
This
may be yet one more "little thing" that adds up to the big picture of the SSPX softening. But I do not need to cling to this as a softening towards Rome; a dozen other much more disturbing things are already convincing enough. I can separate this as one thing being made right, even if they have ulterior motives of playing up to conciliarists. Objectively speaking, clearing this up for all consciences, whether scrupulous or lax or somewhere in between, is good.
Knowing the letter of the law doesn't necessarily mean one is following it. It just means you know it. From that starting place you can choose to follow the spirit.