Perhaps you don't want to make it a priority convincing the non-Pelagian BoDers for obvious reason, but to defend their right to hold it even when they know 1) The Church never infallibly teaches it 2) Council of Trent doesn't teach it 3) There are infallible teachings that oppose the BoD theory (eg., St. Siricius, OUM,...) would be to defend bad-will and obstinacy. Any error regarding the faith is very serious, whether it is notorious or not.
I think you've imbibed too much from the Dimonds regarding "bad will and obstinacy." Most people who adhere to BoD do believe that the Council of Trent taught it and accept it on those grounds. St. Alphonsus thought that Trent taught it. People who believe they'er adhering to Trent and to the teachings of 3 canonized Doctors of the Church are not necessarily of bad will. From where they stand, it's Ladislaus (or the Dimonds or Father Feeney) vs. Trent, St. Thomas, St. Robert Bellarmine, and St. Alphonsus. I'm not going to call anyone "bad-willed and obstinate" for preferring those teachers over my opinion.
Those Doctors too were aware of the dogmatic sources, yet they made distinctions they believe allowed them to be reconciled. I strongly disagree and have disgreed for a long time, and I make my case for why I disagree whenever it's called for. But I'm not going to spend my time huffing and puffing against someone who believes it's possible that a Catechumen could be saved by BoD. As Rahner pointed out, the extension of a BoD to catechumens was only made based on the notion that Catechumens were already joined in a way (albeit partially) to the Visible Church.
I'm not going to waste a lot of time arguing with someone who holds a theory of BoD that does not damage the Tridentine ecclesiology of the Church being a Visible Society. Admittedly, very few BoDers hold such a position about BoD. But the few I run across, I am in no position to denounce as bad-willed and obstinate simply because they don't buy my arguments nor those of the Dimonds. At the end of the day, I'm a nobody and so are the Dimonds.
Now, there are some who primarily adhere to BoD because, quite frankly, they don't like EENS doctrine, based on various emotional reasons, and these types are easily spotted. There's certainnly an element of bad will in those cases.
Basically, the Dimonds believe that if they can make a syllogism from a dogmatic source to their conclusion, that means that their conclusion is binding under pain of heresy as well. This is their chief mistake. They don't understand the theological notes. And you yourself use the term "error regarding the faith" very loosely. There's a huge difference between an error/mistake regarding a matter of faith, and a theological error in the sense defined by theologians. Strict theological error is a grave sin, but a loose "error" or "mistake" is not necessarily grave. Nor would the Church have canonized as Doctors of the Church men who taught a theological error in the strict sense. That would have eliminated them from consideration if not from canonization then certainly from being given the title of Doctor.
Now, the core error of our day is ecclesiology and soteriology, and indeed it's the notion of BoD that was gradually extended to use as a weapon to attack and undermine ecclesiology and soteriology. So the temptation is to attack BoD per se rather than the illegitimate extension of BoD. But I refuse to oversimplify it that way and then be in the business of declaring people "obstinate and bad-willed" heretics where the Church has not done so. I will not usurp the authority of the Church in that regard.
With that said, this crisis is the will of God, and He allowed the youthful mistake (later retracted) of a St. Augustine to then be picked up by St. Bernard, then St. Thomas, and then St. Robert and St. Alphonsus, to be amplified over time into the root cause of this testing of faith. Without BoD, there would be no crisis of faith today. I strongly disagree with these Doctors, and I have taken many pains (and considerable amounts of time) to explain why, but I have no authority to bind consciences and neither do the Dimonds. And that is their major mistake, and sadly it leads to a schismatic attitude. I pray for them because they have done much good, but they could do even more good if they were to realize their serious mistake regarding this attitude.