I've talked to my family about MY wishes and they've told me about theirs. My family believes you don't need to take anything with you to the grave, so what can be used, let it save a life. A cadaver liver saved our friend's life and a cornea transplant will let another friend see her babies clearly for the first time in their whole lives. Not receiving a heart in time meant my SIL and late BIL buried their firstborn when he was just 4.
At this point, nobody who I would have a say about doesn't want to be a donor. But those are discussions to have with the person long before the time comes. Ultimately, I would hope that my DH and mother would respect my wishes to help someone, though my goal is to wear everything out myself first.
If someone was strongly against donation, I'd tell him/her to make a living will and put someone else in charge of that vote for the doctors, thereby respecting them, but not making the call that I might struggle with.
Edit to add: If someone was lurking, I'd find out how to remove them. Harassing the nearly dead is disrespectful to the patient and the family.