JWs: why not blood transfusions for infants?

I understand your reasoning about blood transfusionseven if I don't agree with it . But if an infant can't be baptised, why can't it receive a blood transfusion? what effect would a blood transfusion have on it? It hasn't chosen to do something against God's will. Presumably if the child decides to get baptised as a Witness the baptism will make up for the transfusion. I'm interested in theological reasons, not practical ones about whether blood transfusions are good medicine.