[CM]

The Church's own theologians teach it in moral unanimity. The theological truths (Gladius) and conclusions are required to be held by all Catholics. See Tuas Libenter.

Theologians are not infallible.  And when theologians teach a doctrine contrary to the Extraordinary Magisterium, they are teaching heresy.

If you mean to imply that because theologians teach it with unanimty that we are bound to believe it despite contradiction to the Extraordinary Magisterium, then you are crazy.

Besides Pope Pius IX, in Tuas Libenter does not say that just because theologians hold to something unanimously it is for that reason binding.  Far from it, Tuas Libenter states that we are to hold decisions pertaining to doctrine, issued by Pontifical Congregations, and doctrine held by the common and constant consent of Catholics as theological certainties, to deny which is censurable, but not heresy.

You can hardly argue that baptism of desire fits in here.  Why?  Because for one, the ancient, common and constant Tradition of the Catholic Church did NOT consent to Christian burial for catechumens who had died without baptism, nor for offering sacrifices on their behalf.  This in itself indicates that the Church has always believed that those who die unbaptized cannot be saved.

And then of course, there are the definitions of the Roman Pontiffs.  More on that in a sec.

Pius IX says you MUST hold these theological truths (Gladius) and conclusions.

Yes, but obviously he did not teach that such could contradict the ex cathedra decrees.  If a proposition is contrary to the definitions of the Church, it is heretical, and the person who believes it is not Catholic (Leo XIII, Satis Cognitum).

In fine, rejecting baptism of desire as a proposition in direct opposition to multiple dogmatic decrees does in no way render one a heretic, nor does rejecting the teaching of a saint who taught such a contrary doctrine.

But rejecting a teaching given the theological note of THEOLOGICALLY CERTAIN is a mortal sin.

Rejecting a the meaning, once declared, of an ex cathedra decree is the mortal sin of heresy.  A person refuses to do so, and even if he appears to fall under the condemnation you have described, is in fact committing no sin at all.

It is a clear teaching of Pope Pius IX that we are ever to hold to the very meaning conveyed in the words of the ex cathedra decrees themselves. Pope Pius X teaches that to go against this notion is Modernism.

Yes, but this does not guarantee YOUR infallibility when reading the decrees. The Church explains them, and you DISAGREE with the Church's own authorities.

You are forgetting, as most people do, that the Church's authorities have a hierarchy, which must be obeyed.  This hierarchy applies for the teachings as well.

At the BOTTOM of this hierarchy are the theologians.  Then we have saints and bishops, Doctors of the Church, Fathers of the Church.

Next, in the realm of infallibility, we have the Ordinary and Universal Magisterium.  On the same level, we have the definitions of the Extraordinary Magisterium, the ex cathedra decrees, which must never be abandoned under the specious pretext of a more profound understanding.  A person who willingly teaches contrary to this, no matter how much support he may gain for his doctrine, is not Catholic, and neither is his doctrine.

These decrees, which eliminate the possible belief in baptism of desire, are written in SIMPLE language, that is easily understandable, and admits of no exceptions.

A person MUST deny the objective sense of these decrees to believe baptism of desire.

It is naive to think that heresy does not often have its beginning within the visible confines of the hierarchy.  It is even quite possible that a pope, though he may legislate against a heresy, can either by omission or even by commission allow the spread of false doctrines, and yet so long as he does not publicly teach the doctrine, he is still pope.

The Apostle warns that such things can and will happen.

I know that, after my departure, ravening wolves will enter in among you, not sparing the flock. And of your own selves shall arise men speaking perverse things, to draw away disciples after them.

How many disciples has the line of antipopes of the 20th century drawn after itself?  How many people are now more concerned with doctrines and philosophies which have been inculcated in the Summa, which itself is fallible, and how many people regard it as the be all and end all of Catholic doctrine?  It is not.  It contains heresies, propositions which have been summarily condemned by the ordinary authorities in the Church, like the Council of Carthage on limbo, for example.

In a world so turned upside down by rampant Modernism, if something doesn't jibe with Scripture, Tradition and the definitions of the Church, then it should be discarded and trampled underfoot.