Actually, the blood/alcohol analogy is correct as far as consuming any substance by needle or by mouth.
That's just plain ole stupid.
Here's a substance: potable water
If you drink potable water it hydrates your tissue, which is a good thing. If you transfuse potable water it kills you, which is a bad thing.
Here's another substance: alcohol
Doctors who've advised a patient to abstain from alcohol do not abstaining from transfusing alcohol to the same patient if the administration protects the patient from death.