Why can Jehovah’s Witnesses accept 100% of blood fractions and benefit from the blood that others donate, but are not donating blood themselves? Would not giving blood to help save others’ lives, including the lives of your spiritual brothers and sisters, be the loving and Christian thing to do?
Some weeks ago my sister asked this question, and the elders answered it based on an Old Testament principle. So, according to them, Jehovah let israelites to sell carcasses of unbled animals to foreign gentiles. So, the same principle applies for the current people of God. Witnesses can take the permitted blood fractions from wordly people, but they (the witnesses) can't break God's law on blood by donating it.
Of course, my sister disagreed, because she said "we are not under the Law of Moses". But they answered: "some principles remain".