CathInfo.com

I believe there are still FSSP priests who were originally ordained by SSPX bishops so the idea that there could be an FSSP priest that is "certainly valid" from the standpoint of Trad Catholicism is comprehensible.  It seems like the debate comes down to whether attending a mass offered by a priest that endorses Vatican II/in an organization that theoretically accepts the NO, it itself a dealbreaker or not.

I believe there are still FSSP priests who were originally ordained by SSPX bishops so the idea that there could be an FSSP priest that is "certainly valid" from the standpoint of Trad Catholicism is comprehensible.  It seems like the debate comes down to whether attending a mass offered by a priest that endorses Vatican II/in an organization that theoretically accepts the NO, it itself a dealbreaker or not.

Also, since the new mass is a sacrilege (at worst) or a heretical, anti-Trent liturgy (at best), then you have to analyze the effect of such a non-catholic rite on the indult church itself, per canon law.  Or, it's illicit (because it's contrary to Quo Primum).  Or it's invalid (because the priests are invalid).

a.  the new mass as a sacrilege -- canon law says that a sacrilege (especially repeated ones) desecrates the church and catholic worship (TLM) isn't allowed there.
b.  the new mass as a heretical liturgy -- canon law says that you can't attend masses where the priest publicly adheres to heresy, so any "indult" priest who accepts V2/new mass (which ALL indult communities do) is thereby off-limits to attend/support.
c.  the new mass is illicit -- Quo Primum disallows ANY rites besides the 1962 missal.  Any priest who openly accepts the new mass/V2 is an illicit-supporting priest, and canon law disallows attendance/support of such.
d.  the new mass is invalid -- priest of indult communities are doubtfully valid.
e.  All of the above.  ??  Quite possible.

The indult mass is either a sacrilege (i.e. protestant/lutheran service pretending to be catholic) or it's a heretical liturgy (i.e. Arianism or early Anglicanism).

Canon Law has rules for either situation.  People act like the "indult" is some "new situation" that the Church has never dealt with before.  They act like there's no rules in place, so therefore they can make their own decision.  Wrong.

The indult is quite possibly wrong for all 4 reasons above.  Canon Law has rules against all 4 situations.  You cannot attend, except in emergencies.