if the state can't force you to be an organ donor after your death, it shouldn't be able to force you to be an organ donor before your death. if you can't be forced to give even a pint of blood for half an hour, you shouldn't be forced to give up your uterus for nine months. if your alcoholic father can't demand you give him half your liver, if the red cross can't just demand your blood, if those wig making companies can't demand your hair, no one should be able to demand your reproductive system.
even if a fertilized egg is exactly as much of a person as a twenty one year old citizen, no one else in the world should have a legal right to make use of your body parts without your express consent.