To plays devil's advocate there are inconsistent standards of what constitutes dead many established decades ago and whereas some folks are obviously by any standard a potato others including by standards they themselves elect are defunct in ways that we understand far less eg not able to initiate breathing on their own or not capable of regaining consciousnesses. Due to our lack of complete understanding there have been cases in which people were taken off the ventilator to die and spontaneously started breathing. EG our original analysis was obviously incomplete.

What is experienced if anything by those near or even post official death is also an interesting open question. Experiments involving flooding pig heads dead for > 1 hour with oxygenated liquid have shown some sign of electrical activity in cells for instance. We don't even know what the subjective experience of people being operated on really is other than obviously NORMALLY they don't consciously form memories or have control of their faculties.

All of that said organ transplants save so many lives and it is a voluntary process. If you have any concerns whatsoever you ought to think hard about it and make your wishes expressly known rather than blanket shutting the door on saving those lives. I am an organ donor. I have faith in my family to make intelligent decisions if I'm not able to make them.