We do not need our bodies once we leave this world regardless of what you think happens after we die. We should be focused on curing diseases and extending the life of living humans. Science would go so far if we used human bodies after death instead of requiring people to give consent to something they don’t need.
No one person can make that determination or all of us. Also, have you looked into what actually happens when a body gets donated. Here is John Oliver’s investigation:
https://youtu.be/Tn7egDQ9lPg