I had a friend who died at 28 waiting for a kidney. He had more than one friend offer to get tested to see if they could give him one, and he always said no because he didn't want them ever to risk going through what he did. I don't know that I think that was the right decision either, but I understand why he made it. It's not a small thing! Even if everything goes perfectly, *you still only have one kidney*. You do have to live with restrictions and take special care to protect your health, because if that one kidney gets damaged you have no backup.
Like, I would happily do it for someone I loved - giving a kidney to my friend would have been totally selfish, I would have done it because I didn't want to lose him - but it is a *hell* of an ask for someone who has never been kind to you!
Plus, you know, you are the boss of your internal organs, no one has the right to demand that you give away a piece of your body.