It doesn't matter that you aren't sure, and it doesn't even matter if most people agreed with you. Around 60 to 70 million people die every year globally, so if even a tiny fraction of these were willing to take part there would be sufficient numbers for a statistically significant study.

In any case, the fact that a significant number of people opt for organ or body donation suggests they are willing to allow their deaths to be useful to others in some way.