The problem with Blood Transfusion is the problem with anything else you take into your body: quality control.
You can get very sick from a salad bar with lax hygienic oversight.
Competency is competency from medical treatment to driving a car on the freeway.
Secondly, a medical emergency creates a level of stress on any person involved. But, Jehovah's Witnessess have an added layer of anxiety unnecessarily burdening them at such a time: they are in the grip of a terrifying fear of being expunged by their God if they violate the Watchtower policy.
I've gone into great detail before about the Watchtower policy itself. It is a blatant and deliberate publicity stunt which takes the rather simple prohibitions of the Laws of Noah for Gentiles on murder (abstain from blood=do not murder) in order to paint Jehovah's Witnesses as Super Christian Martyrs. We can thank the contrarian tastes of Judge Rutherford and the macheivellian mind of Fred Franz for the resulting doctrine.
The ethical question is simple, but, not simple-minded.
Life only has value when it has purpose
For ordinary humans self-preservation is the beginning of all other values.
A dead person cannot worship a living god.
When death becomes a valuable purpose it exposes a core insanity.
The (Watchtower) blood policy turns this on its head. Abstaining from blood was life affirming to Christians and Jews in the 1st Century because it was a call for preserving human life by not shedding blood in murder. The Watchtower has diabolically reversed this into a death affirming policy by making martyrdom more important than a living worshipper.
The actual "respect for Jehovah" blood issue was contained in the prohibition on "Keep yourselves free from things strangled..." because the blood was not poured out.
Ask yourself a simple question.
Why would Christians not be warned about murder if it weren't contained in "abstain from blood" (corresponding to the Noahide Laws)?
The Watchtower Blood issue is a huge neon sign blinking on and off over a pawn shop where people offer their lives and the lives of their love ones for a cheap pawn ticket that buys them a martyrs death for no other reason than that they've been lied too about what is really valuable. Life is the greatest value; not approval from a book publishing company in Brooklyn!