SSPX = certain that they are always valid if done by the book.
Sedes = certain that they are always invalid.
Us = certain that they are always doubtful.
Just to clarify the above, for everyone else who is reading. Stubborn, your classification of the above 3 views is incorrect.
1. There are really only 2 views - positively doubtful or no doubt. This is the crux of the issue -- do the new rites have positive/factual doubt? Yes.
a. The sspx admits there is doubt, but says the doubt is "minimized" when you use book A vs book B, C or D.
b. The sspx ignores other doubts (deletion of the word "ut" in the ordination rite) and the episcopal/bishop consecration rite, which is a total joke and full of doubts.
2. The Sedes say they are "always invalid" because they are speaking practically, i.e. how canon law tells us to act with doubtful sacraments (i.e. treat them as invalid).
a. No Sede cleric is going to say that they are the Church, or that they are infallible, or that they know with 'moral certainty'. Come on. That's not their argument.
b. Their argument is based on practice (i.e. how do we act?). Which comes from canon law.
3. The "3rd" way of thinking is no different than the Sede mode of thinking. Positive doubt exists. What then?
a. Canon Law says that when there is positive doubt (i.e. doubt based on facts), then we MUST take the safest course.
b. We are not allowed to attend, support or use doubtful sacraments, WHEN THERE ARE NON-DOUBTFUL SACRAMENTS AVAILABLE.
c. To use doubtful sacraments (when non-doubtful/certain sacraments are available) is a GRAVE sin.
d.
Ergo, practically speaking, canon law FORCES us to treat doubtful sacraments AS INVALID. They are off-limits, under penalty of grave sin.
e. You can only use doubtful sacraments IN AN EMERGENCY.
f. This would also apply to the masses of doubtful priests,
which is why the Indult is off-limits and a grave sin. You cannot attend doubtful masses, by doubtful priests, without sinning, per canon law.
So there is no difference, practically, (i.e. real world, how we act) between the Sede view and your 3rd view (i.e. certain there are doubts).
There are only 2 views:
1. New-sspx/Indult/V2 view -- the new rites are valid, with small exceptions.
2. Traditional view -- the new rites are doubtful and (per canon law) off-limits and treated as invalid.