A few days back, I published a post entitled "Was Chasam Sofer Actually Correct?" This was in reference to Chasam Sofer's famous ruling to ignore recommendations to wait three days before burial amidst concerns that people were being buried alive. I noted that this ruling was bizarre in light of Chasam Sofer himself suggesting that Chazal took their definition of death from the gentile physicians of their era; if so, why shouldn't Chasam Sofer follow the medical science of his era? In order to account for the strangeness of his ruling, I suggested that Chasam Sofer was motivated by meta-halachic considerations involving reacting to Reform - similar to Maharam Schick's opposition to any compromise on metzitzah b'peh, which involved arguments and claims that are simply false, but can be understood in light of it being a meta-halachic issue.
Now, some people saw it as unacceptable to claim that Chasam Sofer was being either deliberately or unknowingly dishonest in his responsum. I can understand that objection (although, without an explanation of how his responsum is coherent, I don't think it helps save Chasam Sofer.) Fortunately, subsequent to writing the post, I discovered that Chasam Sofer had a follow-up letter which was not published along with his original responsum - in which he explicitly admits that his statements were incorrect from a strict halachic perspective and in which he justifies saying them due to meta-halachic considerations!
The original responsum was written to Maharatz Chayes. Maharatz Chayes responded to Chasam Sofer's claims regarding the Biblical weight of the prohibition against leaving the dead unburied, insisting that these claims were simply not true. And Chasam Sofer replied that, technically speaking, Maharatz Chayes was absolutely correct, but in light of the fact that nowadays many people are not concerned about rulings that are "only" rabbinic, one should elevate their status and claim that they are min ha-Torah. (I had long been aware that this was Chasam's approach in general, but I never previously knew that he stated it specifically with regard to this issue.)
It is not surprising that when Chasam Sofer's responsa were published, this letter was left out. Fortunately, Maharatz Chayes printed it in his own work, and you can read it here. Pay attention to the footnotes, where Maharatz Chayes sharply disputes the notion that one can make incorrect claims about the status of halachos in order to motivate people to keep them.
(Personally, I can sympathize with both points of view. But in the long run, I think that Chasam Sofer's approach backfires. This is especially true in the modern era where there is more access to information. Sooner or later, people will find out that they are being deceived - and this deals a devastating blow to their confidence in rabbinic authority.)
The letter does not address the question of why Chasam Sofer attributes final authority to Chazal's definition of death even if they took it from gentile physicians. But it seems most reasonable to say that, either consciously or subconsciously, the same factors were at work. Because in matters of life and death, no posek would ordinarily rely on the physicians of antiquity over those of today.
The only remaining puzzle that I have is why so many halachic authorities incorporate this responsum of Chasam Sofer into their position on brain death. Of course, my primary objection is the fact that Chasam Sofer was not saying anything at all about whether the presence of respiration (and/or a pulse), in the absence of brain function, is sufficient to rate a person as being alive. But aside from that, the revelation of the extreme meta-halachic aspects of his position should surely weigh against utilizing his stand, for those who feel that such meta-halachic considerations should not play a role today.