“However, they sent me this image which apparently not only disproves that a deceased catechumen can be saved, but proves that such a belief is heresy.”

Sorry, I've been a bit distracted, and the answer to a PM like that could be very lengthy, so I hadn't had the time/opportunity to respond.

Even in a BoD, one MUST hold that Baptism remains the instrumental cause of justification, operating via the votum for it.  That votum would in fact just be the means by which the graces of Baptism are applied to the soul.  To say otherwise would be to assert that people can save them selves by their own merits, ex opere operantis ... which contradicts the essence of Trent's teaching regarding the Sacraments ... and is in fact Pelagianism in a nutshell.  This is precisely what that "Chapter 8" in your citation above says.

That is why St. Robert Bellarmine and the post-Tridentine theologians were very careful to state that the souls who are justified though BoD receive Baptism in voto ... not that they are saved without the Sacrament or independent of it ... since Trent dogmatically taught the necessity of the Sacrament for salvation.  To say that someone can be saved without the Sacrament of Baptism is indeed heresy.

Ironically, it's this distinction made by these theologians that the Dimonds also miss in alleging that BoD (even that of St. Robert Bellarmine) is heresy.  Indeed, if someone said that people can be saved without the Sacrament, that would be heresy, a direct contradiction of Trent.

Now, since the first generation or two after Trent, the language became sloppy, to the point that most modern BoDers do hold a heretical view of BoD.  But there is a view which, when properly articulated, does not lead to heresy.

Now, I do not believe in BoD.  I don't see a need for it, since God's providence is not bound by "impossibility".  As St. Augustine taught, it is "not Catholic" to suppose that God could be prevented from bringing the Sacrament to His elect.  Also, I hold that the character of Baptism is essential for salvation, since it is in fact the supernatural capacity to see God as He is (i.e. the beatific vision), which we lack the faculty to do by nature (similar to how a priest is transformed by the character of the priesthood).  But to say that it is inherently heretical is wrong.  One can still find way to maintain the necessity of the Sacrament of Baptism while holding a certain form of BoD.

This is in fact the distinction between the two different understandings of Trent.  Those of us who do not believe in Baptism of Desire hold that the votum is a necessary (but insufficient) cause of justification, while the other (more popular view) is that the votum is a sufficient cause of justification.  I argue that Trent's language of "cannot without" clearly teaches necessary cause rather than sufficient cause.

Sorry, I've been a bit distracted, and the answer to a PM like that could be very lengthy, so I hadn't had the time/opportunity to respond.

Even in a BoD, one MUST hold that Baptism remains the instrumental cause of justification, operating via the votum for it.  That votum would in fact just be the means by which the graces of Baptism are applied to the soul.  To say otherwise would be to assert that people can save them selves by their own merits, ex opere operantis ... which contradicts the essence of Trent's teaching regarding the Sacraments ... and is in fact Pelagianism in a nutshell.  This is precisely what that "Chapter 8" in your citation above says.

That is why St. Robert Bellarmine and the post-Tridentine theologians were very careful to state that the souls who are justified though BoD receive Baptism in voto ... not that they are saved without the Sacrament or independent of it ... since Trent dogmatically taught the necessity of the Sacrament for salvation.  To say that someone can be saved without the Sacrament of Baptism is indeed heresy.

Ironically, it's this distinction made by these theologians that the Dimonds also miss in alleging that BoD (even that of St. Robert Bellarmine) is heresy.  Indeed, if someone said that people can be saved without the Sacrament, that would be heresy, a direct contradiction of Trent.

Now, since the first generation or two after Trent, the language became sloppy, to the point that most modern BoDers do hold a heretical view of BoD.  But there is a view which, when properly articulated, does not lead to heresy.

Now, I do not believe in BoD.  I don't see a need for it, since God's providence is not bound by "impossibility".  As St. Augustine taught, it is "not Catholic" to suppose that God could be prevented from bringing the Sacrament to His elect.  Also, I hold that the character of Baptism is essential for salvation, since it is in fact the supernatural capacity to see God as He is (i.e. the beatific vision), which we lack the faculty to do by nature (similar to how a priest is transformed by the character of the priesthood).  But to say that it is inherently heretical is wrong.  One can still find way to maintain the necessity of the Sacrament of Baptism while holding a certain form of BoD.

This is in fact the distinction between the two different understandings of Trent.  Those of us who do not believe in Baptism of Desire hold that the votum is a necessary (but insufficient) cause of justification, while the other (more popular view) is that the votum is a sufficient cause of justification.  I argue that Trent's language of "cannot without" clearly teaches necessary cause rather than sufficient cause.