Welcome to JWD and thanks for your detailed discussion of some of the issues that bear on taking blood. As a matter of interest to the forum I attach a portion of Rolf Furuli's correspondence which is pertinent to your discussion :
PRINCIPLES ARE ETERNAL - LAWS DO CHANGE
There are very few laws that govern the Christian way of life, but many principles. A principle is a ‘fundamental truth’, and fundamental truths in connection with God never change (Malachi 3:6). Laws are often an application of one or more principles in a restricted situation. This is the reason why three of the laws mentioned in Acts 15:28, ‘to abstain from fornication, things strangled and blood’ are based on the very same principle, namely, ‘God is the source of life’ (Psalm 36:10). For example, in order to give a child the best possible environment for growing up to become a balanced and happy human being, sex between persons is restricted to marriage. For instance, a couple living together without being married, may have a more stable relationship and show more love for one another than some married couples, but they are not willing to take the final step, a legal marriage where they are permanently bound to one another. Thus any children may not have the best possible environment, and the Witnesses therefore view sexual relations inside such a union as fornication.
The different situations of ancient Israel and the Christian congregation may also help us realise the difference between laws and principles. It is obvious that principles will be applied differently (materializing in particular laws) in a society which is restricted to a particular area (Palestine), where the literal temple of God stands, and where the laws of God regulate both the secular and religious life, than among the Christians who are spread around the world, who have no literal temple, and who are bound by the secular laws in their country. However - and this is very important - principles whose application are not affected by the differences between Israel and the Christian society will materialize in exactly the same laws in both societies. For instance, the principle that only the Creator deserves worship is not affected whether the people of God is a nation with literal borders and a temple, or whether they are spread around the globe and worship without the help of anything visible. Some of the laws of Moses, therefore, are binding for Christians, not because they are a part of the Mosaic law, which is abolished, but because they build on principles which are not affected by the situation in which the people of God is.
THE PRINCIPLES ON WHICH THE PROHIBITION AGAINST BLOOD ARE BASED
Connected with the principle ‘God is the source of life’ is another principle, namely, ‘the life of all creatures belongs to God’ (Ezekiel 18:4). Based on these two principles the ‘use’ of life has been and is greatly restricted: 1) life should only be given to others inside marriage, 2) the life of human beings should not be taken (except when it is directly commanded by God), (Genesis 9:6), 3) when animals were slaughterd for food, their life, represented by their blood, should by treated in a way showing that the life is given back to God (Leviticus 17:10-12) [Note that in the days of the tabernacle it was not enough to pour the blood out on the ground, but it should be poured out at the entrance of the tabernacnle (Leviticus 17:3-9). This shows that the pouring out of the blood was a religious act; it indicated that the life was given back to God.] Thus in ancient Israel the blood of humans should not be spilled except when God commanded it, and the spilled blood of humans should not be used for anything at all. Animals could be slaughtered for food, but their blood should not be used. There was, however, one exception: blood was used on the altar because "it is the blood that makes atonement" (Leviticus 17:11). In Israel animals were sacrificed for the sins of the people; in the Christian arrangement Jesus was offered once and for all (Hebrews 10:10).
Blood has represented life in the days of Noah, under the Mosaic law, and in the Christian order. This means that the regulations of the use of blood (based on the mentioned principles) are not affected by the situation of the people of God. This is shown throughout the Bible where the only legitimate use of blood [by the words «use of blood» I mean of course the use of the blood of other creatures and not my own. The arguments of Daniels that I use my own blood and therefore am inconsistent when I say that blood cannot be used, are strange indeed] is on the altar (animal sacrifices in Israel and the sacrifice of Jesus in the Christian order). All other uses are prohibited, not by a long list of prohibitions, but simply by the fact that blood belongs to God and that he has stated that it should be poured out on the ground. So, because God is the source of life and life belongs to God, we are not allowed to give life to others through procreation except inside marriage, we are not allowed to use blood in any way to sustain our life by eating it, and we are not allowed to use blood for any purpose. [While I in principle see no difference between eating and a blood transfusion, my custom is not to use this in conversations regarding blood, because it does not cover all situations. For me, the absolute prohibition of any use of blood is the ultimate reason for refusing to take haima into my body, and this I convey to others.]