Generally, I think if a patient needs blood transfusions there's a bigger and more immediate life-and-death problem right there. I think allergies would be preferable to death.
Is my understanding correct? I hope blood transfusion hasn't become a routine procedure these days.
I don't think GC was suggesting that we stop blood transfusions, but rather that we do better tracking to improve our understanding in a way that normally would be unethical (if not for the fact that, as you say, blood transfusions are a life-saving intervention).
Before the 1990's but not anymore. The contaminated blood scandal in the United Kingdom (https://www.infectedbloodinquiry.org.uk/) and a lot of papers showing benefits to avoiding blood loss in the first place have changed practices. We haven't eliminated the use of allogeneic blood transfusions but they're indicated a lot less than they used to be.
Is my understanding correct? I hope blood transfusion hasn't become a routine procedure these days.