Why is donating a hand any different to donating a pancreas? actually I think that receiving a hand is different to receiving a pancreas. Because a hand, face etc is an external part of someone else.
It’s not remotely comparable to an internal organ which just works alongside your other organs in the same way your existing one does. you don’t think about it, but a hand is there. It’s visible and is someone else’s.
In fact I would feel weird about shaking the hand of someone which was in fact not their hand.
Our external self is very much a part of who we are.
I have various bits of technology/kit in my chest which keep my heart beating for now, or at least improve its functionality and prevent it from stopping. I don’t give those things a second thought because they’re just there. I don’t feel them, (well I feel my ICD in that there’s a small outline of it, and I feel it if it paces,) but as a rule it and the other stuff (mitraclip as I was ineligible for a full valve replacement) is just there.
Similarly if I receive a heart I will know it’s there, but as time goes on it will just become a part of me.
But a hand? A face? You look in the mirror at yourself and it’s someone else’s face, or you go to put rings/nail varnish on and it’s someone else’s hand. Sorry but no.