Try asking a Jehovah's Witness why blood is not allowed, but fractions made from blood are allowed. I would bet money 98% of them cannot even tell you the wacky line of reasoning the Watchtower uses. But they will throw their life away because of it, convinced they it is because it goes against their conscience. Really, they have been conditioned to fear it. My ex husband refused blood even though he had been disfellowshipped for twenty years. I was still in the lie at the time and I thought he was crazy. His hemoglobin was down to three due to internal bleeding from Chrons disease. A nurse friend told me that that low of a count is not compatible with life. He lived, barely, but his recovety was much slower because of it, he was disabled for a year, didn't work for three. I had no illusions that he was doing it out of loyalty to God or the organization, he was simply afraid.
Personally I think the organization has backed them selves in a corner with this one. They will continue to move toward allowing blood, at some point there will be a blood product that will be closer to real blood, but different enough that they can claim it's OK, or there will be "New light" that blood is OK after all.