As a religion, WT and JW's are within their right to state a belief that using blood is not acceptable to God. Any qualifications they might possess is in regards to belief, sin and what is acceptable to god.
Problems arise when WT goes beyond religious matters to teach, advise and counsel on medical matters for which they are not qualified in. As previously stated, to offset liability, WT commonly mention a person may die if they don't follow their Dr's advice regarding treatment which may include blood. They also state acceptance of blood is not a guarantee a person will survive. JW's will often accept WT information as fact without doing further research from other sources.
As JW's believe God requires his people to abstain from blood, they then hope for resurrection if they should die while faithful to God's requirements, which suggests they may not receive resurrection if they are not faithful.
A person's beliefs are emotional and can greatly influence their decisions, often to their own detriment. Even if a JW wishes to accept blood, there is often fear of punishment, if not from God but from the org they and their family are members of.
Ultimately, a person needs to do what they consider to be correct for them and their medical situation at the time. No one else will live (or die) by their decision. If the person requiring treatment is a minor child, and the parents do not consent to the prescribed therapy, the courts will often intervene to make a decision on facts and medical advice for the child's benefit, not on beliefs or emotions.