You might want to reconsider and do a little research. I read your post and curiosity is prompting me to delve into the organ donor facts a little deeper.
My philosophy is simple: I don't need this body when I die, "so dispose of it as you will" (as the Klingons would say).
Research, science exhibit, transplant materials, part'n'pieces here'n'there - if I can be put to good use for even 1 person when I'm gone, that's just carrying on what I try to do now.
I had always thought that some body parts might not be cancer- or whatever-prone, or at the least wouldn't carry any rogue properties with them. Even so, don't they do pretty comprehensive compatibility studies before they use the parts? And what they can't do now, they be able to do by the time I die, so I'll sign the card in anticipation of knowing they're inventing even better science as I write.
Even if body parts are found to be faulty or incompatible after they're used, the recipients still would get some living-longer or living-better use out of them. There's even the possibility of another transplant, too.