Jehovah's Witnesses believe that having a blood transfusion is the same as eating blood. According to the Bible, eating blood is not allowed by God.
However there are several reasons why blood transfusions are not the same as eating blood. Here's one.
According to the Bible, when an animal is killed so we can eat it, the blood represents it's life that it gave for our benefit.
However in the case of blood transfusions, the donor is not killed. Blood is donated in small quantities. No one donates all their blood and gives up their life. Because of this, donated blood does not represent 'the life' of a person.
No one walks into a blood bank and says, 'drain all the blood out of me. I want to die to save someone else's life'. Therefore, donating a pint of blood does not represent anyone's life. They still get to keep their life.
In essence when a person donates blood, they are giving the gift of life without sacrificing their own. They are being 'Christ-like'. They are loving their neighbor without judgment as to whether a person is worthy, or what their religious or moral beliefs are. Luke 6:27-42
Refusing to accept the gift of life and risking one's life needlessly does not honor the Bible's position on doing 'good'. Jesus used every opportunity to heal the sick, even if it meant breaking the Mosaic law.
As you read the articles listed at the bottom of this page, you'll see that refusing blood transfusions is the wrong way to interpret God's message.
God gave us life. As good stewards of God's gift, it is up to us to take care of the body he gave us and protect the lives of our neighbors if we are able to.
If a life saving procedure is available, refusing it does not honor God. In fact, God may have a heavy heart, watching Witnesses needlessly choosing to die and telling the world that it's 'God's' law, when in fact it is their own law.
It was a mistake to claim they are God's 'channel of communication'. They are not. Some day, the wicked will be judged by God. Until then it's up to us to love and accept people regardless of their beliefs. Love is the way of Christ.