The old Hebraic law of abstaining of blood was specifically handed out as a dietary law
I disagree.
JWs also disagree and if we are going to help them to reason on blood transfusions it is more useful to find as much common ground as possible.
1. Blood was sacred under The Law.
2. Blood represents life.
3. It was a capital offense to use blood for any purpose other than to offer it as a sacrifice on the altar.
4. All of the restrictions about blood are just as binding on Christians as they were on OT Jews.
It doesn't matter if you agree with all four of these points or not. They believe them, and we can concede all of them and start from there.
The key point is this...
Blood is only sacred insofar as it represents a life that has been taken