This is a pretty good article on the matter of “brain death.” Fr. Tad makes the very important point that someone who is actually “brain dead,” by the legal definition, would only be able to have cardiac function retained for a matter of hours to days. Any of the reports of people being “brain dead” for weeks, months, or even years, can not possibly be true, by the current legal definition in the US. I think he is right to oppose any change to the standard, but I think he is wrong to believe that the “medical industrial complex” cares about adhering to anything that would tend to reduce their access to transplant organs.
People in comas, where brain activity is decreased, are at risk of having their organ harvested, the rationale being they will probably be vegetables if they wake up. It is a financial consideration, maintaining someone sleeping in a bed versus selling their organs. They can't wait until someone dies, because the organs die. The organs have to be working, the person has to still be alive.
Yes. There are a whole host of ethical issues. The US legal definition of brain death, which Church authorities have accepted for awhile (I don’t mean to say that the Church has definitively accepted it) defines it as a complete death of the entire brain. I’m not convinced that it is possible to determine this, to a moral certainty. If someone is declared dead according to neurological criteria, that diagnosis could be reconsidered, theoretically. But it can’t be reconsidered if the persons organs are harvested, because a person without a heart is dead, by any standard. Personally, I don’t believe in transplantation of any kind, nor in any form of organ donation.