CathInfo.com

I don't know already, it's the same arguments repeated over and over.

It simply boils down to....
There are those of us who accept the defined doctrines, Scripture, and all the other teachings from the highest authorities in the Church (and everything associated with those teachings that we must believe), and therefore cannot in good conscience accept a BOD because a BOD contradicts all those things regardless of the lesser authorities (great saints, catechisms etc.) who taught otherwise.

And there are those who believe defined doctrines, John 3:5 etc., but are convinced that all those teachings have exceptions built into them somehow, which apparently, is why they not only see no contradiction whatsoever, instead they're convinced a BOD is a doctrine of the Church. 

How?  According to St. Fulgentius, it's because God would keep them alive until they could receive the Sacrament on account of these dispositions.

With regard adults who enjoy the perfect use of reason, persons, for instance, born of infidel parents, the practice of the primitive Church points out a different manner of proceeding... On this class of persons, however, the Church does not confer this sacrament hastily: She will have it deferred for a certain time; nor is the delay attended with the same danger as in the case of infants, which we have already mentioned: and should any unforeseen accident deprive adults of baptism, their intention of receiving it, and their repentance for past sins, will avail them to grace and righteousness." (p124,125 of the text)
 

5. Born again of Water.] As no man can enter into this world nor have his life and being in the same, except he be born of his carnal parents: no more can a man enter into the life and state of grace which is in Christ, or attain to life everlasting, unless he be born and baptized of water and the Holy Ghost. Whereby we see first, this Sacrament to be called our regeneration or second birth, in respect of our natural and carnal which was before. Secondly, that this sacrament consisteth of an external element of water, and internal virtue of the Holy Spirit: Wherein it excelleth John's baptism, which had the external element, but not the spiritual grace. Thirdly, that no man can enter into the Kingdom of God, nor into the fellowship of Holy Church, without it.

Whereby the *Pelagians, and Calvinists be condemned, that promise life everlasting to young children that die without baptism, and all other that think only their faith to serve, or the external element of water superfluous or not necessary: our Saviour's words being plain and general. Though in this case, God which hath not bound his grace, in respect of his own freedom, to any Sacrament, may and doth accept them as baptized, which either are martyred before they could be baptized, or else depart this life with vow and desire to have that Sacrament, but by some remediless necessity could not obtain it. Lastly, it is proved that this Sacrament giveth grace ex opere operator, that is, of the work itself (which all Protestants deny) because it so breedeth our spiritual life in God, as our carnal birth giveth the life of the world.

As I mentioned before, the Catechism seems to be referring to a situation similar to that expressed in the original Rheims annotation to John 3:16:

The "unforeseen accident depriv(ation)" of the Catechism seems much closer to the contemporaneous Rheim 's description where the catechumen "depart(s) this life with vow and desire to have the Sacrament."