Does any human (however anyone defines it) have the right to use the organs and blood supply of another without that person's consent? Thats another important part of the debate. (And for the sake of argument, no one can tell another person what they do or do not consent to. Consent must be freely given).
I think its kind of telling that the philosophically debatable 'human' becomes the 'crux' of a debate when an actual human with rights of their own is most definately involved.