In my opinion, if the death of a person is certain, hastening that death by a few days to protect the viability of needed organs that will add many years to the quality of life for multiple people is a rational thing to contemplate... It is rational to contemplate. However, on balance, I go with the "slippery slope" position. Using the strict brain death criteria has far less abuse potential. True brain death is not as rare as you suggested in an earlier post.
Practically speaking, the greater good you speak of is being diluted. Many of these organs are being transplanted into patients who, themselves, are "terminal." There is too much money changing hands with the current system.
You could be right, because I am not familiar with the current "brain-death" protocols, but it would seem to me that true brain death would only occur in closed head injuries, and leave out the vast majority of terminal patients who have opted to donate yet are none the less dying for sure within days or hours....
Just my layman's opinion....