Caution is always good.
I follow the lead of a pretty reliable source, the Council of Trent, in looking to penance and baptism together, since Trent uses them analogously, and in the specific context of discussion - sacramental necessity.
Moreover, we are also told in the Holy Office letter:
Again, we have a Magisterial, or at least purported Magisterial, authority using the two sacraments analogously, and in the specific context of sacramental necessity.
Of course there is a difference between the sacraments. If you want to take the difference, apply it to the context of sacramental necessity, and say that the analogy is inapt, by all means go ahead.
It seems apt to me, and to the authors of the HOF and the Fathers of Trent. But perhaps you are on to something.
Shoot.
It was a cautionary
side comment, and it was as to
method not as to
substance (other than peripherally with regard to distinctions in procedural
votum between those two sacraments). As you note above (emphasis added) the parallel is
necessity (leaving aside, for the sake of completing this reply, whether that necessity speaks to justification or to salvation).
The ends sought by/for the soul via the two sacraments are the same, yet the means by which a given soul, as catechumen-subsequently-baptized penitent, obtains these ends at two different moments in time are not (re your citation of Pope Siricius regarding adult Baptism). There appears to be little if any question as to what constitutes the sacrament of Penance. There appears to remain some question as to what exactly (once we depart from the usual form and matter) constitutes the sacrament of Baptism.
If
A is a discrete set while
B is not, then it might be prudent to refrain from stating that
A and
B in all of their respective attributes (beyond
general necessity) are analogous. Otherwise, that would be an opening to avoidable confusion.
As to reliance on Trent, in Reply #13 you said as well:
I see an argument against my position by saying that the Catechism implies that a BoD would apply to all catechumen in such circuмstances. But I don't think it can be read that way, and think my analogy to the sacrament of penance applies.
Might someone not already fully adept in that element of the Catechism infer that the analogy in use here is your reading?
Earlier I also said clearly that I don't pretend to deal with the main topic of sacramental
necessity. I leave that to those with the requisite knowledge, whose diligence toward the subject and whose care for the clarity of its treatment I do appreciate.