A transfusion of foreign blood, also called allogeneic blood transfusion by medical professionals, offers the possibility of transfusing more than just blood. For blood does not only contain red and white blood cells etc., it also carries everything that has entered the organism, such as viruses, bacteria, toxins and much more.
A blood coagulation medication of the Bayer company respectively their American subsidiary Cutter shows an especially tragic example which is to be described as criminal. Its coagulation factors were extracted of donated blood which partly came from HIV positive donors. The extraction process of the coagulation factors did not eliminate the viruses in the products. Despite knowing of the contamination of the products, the company sold them to Hong Kong, Taiwan, Japan and Argentina and "turned" the patients with coagulation disorders into HIV patients too.
Another point is about the misconception that there are universal donors and universal recipients for blood donations. Blood group 0 is said to be universal donor and blood group AB universal recipient. But this is not true. In addition to that, there are not only AB0 blood types but also quite a few more that almost certainly are not compatible with one's own blood. This means that each transfusion is a challenge to the immune system which recognises these incompatibilities and reacts to them.
But as it seems, these "challenges" have hardly played a role in conventional medicine for years.
In Germany, up to 5 million blood transfusions are carried out annually. Considering the fact that one bag of blood costs 100 euros and earns up to 300 euros per patient, all of that times 5 million, it is easy to determine the financial relevance of the blood trade.