All these arguments about why resistance members must leave their perfectly orthodox chapels are ridiculous, strained, and contrived.
Fr Pfeiffer, et al, try to pretend there has been some formal mission statement enacted which disqualifies our attendance in SSPX chapels.
There is not.
Instead, there is a scandalous doctrinal preamble THAT WAS REJECTED.
The preamble is not SSPX policy (thank heavens)!
Certainly Bishop Fellay was willing to sell out, but the plot was foiled (for the time being).
More than this, the resistance WITHIN the SSPX is building, as witnessed by the letter of the 37 French District priests, so the idea that the SSPX is too far gone to save doesn't hold water either.
OFFICIALLY THE SSPX IS THE SAME AS IT EVER WAS.
It is only UNOFICIALLY that it has liberalized.
People who are taking my position and strategy like Matthew for one; not that he got it from me (fight from within; support resistance priests when they come around), are making a difference and rolling back Menzingen's plans.
But to contrive arguments to support an SSPX-wide red light to build your own resistance support base harms souls more than it helps them.
When there actually is some SSPX sellout as official policy (I.e., an accepted deal instead of a failed one), the red light will go up.
For now, everything depends on local conditions.