CathInfo.com

I certainly don’t recognize any “monopoly on the traditional sacraments”. 

You may not recognize it, but it is reality for most people in the US.  Without the sspx, most people wouldn’t have a Latin mass within 2-3 hrs of them.  You can call it a monopoly or top Latin mass producer or just simply, the largest priestly organization.  

… The Society is, at most, a voluntary “pious union of priests,” and was never more than that from its very foundation.

With respect to hollingsworth's comment, I am a little puzzled that no one has yet produced a copy of the actual text of perpetual engagement. Surely it ought to be seen and read before any full-blown attack or defense begins!

From the admittedly less than forthcoming description provided by the SSPX docuмents, one might draw the inference that perpetual engagement differs little, if at all, from incardination. If such is the case, the most salient objection—perhaps indeed the only relevant one—is Matthew's: that the commitment is being demanded from someone too young to know what he is doing or, put otherwise, insufficiently advanced in discernment of his vocation. Again, until the docuмent is read, any response amounts to punching in the dark.

Let's assume for the moment—I repeat, absent evidence of any sort—that what the Society chooses to call perpetual engagement is indeed the rough equivalent of incardination. In such a case, surely "perpetual" ceases to be an absolute. Everything I myself know about incardination from 73 years of living as a Catholic corresponds with what the online version of the old Catholic Encyclopedia says in the article of the same name: "It must be remembered that in canon law a person belongs to a bishop in any one or more of the four following ways: by birth, by benefice, by domicile, or by service. In accordance with this the Church has always maintained the principle that excardination cannot be forced upon a person unwilling to accept it, nor at the same time can it be withheld unless there exist a just reason" (emphasis added). Of course, the encyclopedia has no inherent doctrinal authority, but if it is incorrect in this instance, I trust that someone will step forward to explain how.

As it is a fact that long before Vatican II, priests were regularly excardinated from one diocese and incardinated in another (or were otherwise redirected or laicized), the Society's perpetual engagement would need to be something extraordinarily and unprecedentedly binding to represent the sort of dangerously unbreakable tether that some hereabouts have assumed it is. Once more, I do not discount the possibility that it is, but until docuмentary support for one view or another is forthcoming, no bridge from the possible to the probable, let alone the certain, can be said to have been established.