I see your point.
According to post #213, the marrow is extracted with a big needle -- they aren't cut open. He says in the nineties it was done under general anesthesia, but he is guessing that is more about the comfort of the donor than a necessity. I've given birth to four kids. The first 2, I delivered naturally without any pain killers. The last one, I had a C-section. I'm not saying I'd enjoy it, but I'm thinking I could handle taking a needle to save the life of my brother.