GG,
Setting the risks and benefits of blood therapy aside right at the beginning of your debate was a good step. If one is refusing blood for religious reasons, then, the possible physical risks (or benefits) of medical blood use is a moot issue. JWs will often fall back on that because the WT often uses that in their argumentation. But it is a red herring.
One thing JWs don't appreciate is the fact that in the Bible (both the Noah Covenant and the Mosaic Law) blood is only a symbol for life when the source of the blood has been killed. God gave Noah and his descendants permission to eat animal meat on the proviso that they pour out the blood in recognition of the fact that the life belonged to God. So, the blood only symbolized the life when the life of the animal had been taken.
Similarly under the Law Code, an Israelite could not simply bring a blood sample from his best bull/goat/sheep to the Temple for splashing on the altar. The animal had to be killed first (after the Israelite laid his hand on the animal's head in symbol of the animal representing him). Only then did the blood represent that life and had atoning value at the altar.
On the other hand, if an Israelite found an animal already dead (naturally or from a predator), eating its unbled flesh only incurred ceremonial uncleanness (as opposed to the death penalty if he himself had killed it).
With that understanding, blood transfusions or blood therapy of some sort should, theoretically, incur no blood guilt or wrath by God since no human life was taken. And thus, the blood involved did not symbolize any life. (Like a wedding ring, it only represents a particular marriage when it has been given to someone. A wedding ring in a jewelry store does not represent anyone's marriage.)
Moreover, Jesus said that there is 'no greater love than for someone to lay down his life for a friend.' (Jn 15:13) It would not make sense for the giving of one's whole life to be praised, but the giving of some part (like a pint of blood) to be completely condemned.
Just extending this thought a little: What if the blood product was some derivative of animal blood? That should not be a problem either, especially if it was not whole animal blood (that is, it was a fraction of some sort). When draining an animal's blood it is understood that every last bit of blood would not be drained. Draining it was a symbolic act. And thus, a fraction from animal blood (supposing that the animal had been killed for it) would not represent a disrespect for God's Covenant with Noah. (And in fact, the WT usually has no qualms with such fractions.)
Having said all that, I also agree with some of the sentiments above that JWs are usually taught to be aloof in their thinking with 'pagans.' They probably can't be reasoned with unless something has happened in their lives to start the process of thinking outside the box.
Just as an aside, the WT's often treacherous reasoning can be seen in the Reasoning book under the topic of the Memorial. Under that topic they claim that Jesus' statement about 'eating his flesh' (in John chapter 6) cannot be equated with the bread at the Memorial since at the time of John chapter 6 the disciples knew nothing about the Last Supper. If one were to use that same WT logic, then, the order to "abstain from blood" could not be referring to transfusions since transfusions were unknown at that time. But let a JW try and use that logic. It would only result in a JC.
