Yes indeed they are!
Setting aside the whole question of theology, what indeed are the risks. They are significant enought that virtually any new product coming to market with simlar risks simply would not be allowed to be used. Flurocarbons are officially kept off the market because of a lower increased risk of heart attacks in those who recieve them than the risks associated with transfusion.
The first risk comes from transfusing the wrong types. Okay, we know about that, but despite testing an unknown number die every year from transfusion reaction. I personally know of several who died because they got the wrong type of blood and the nurses who were supposed to be monitoring them didn't do their job. And guess what, neither death certificate listed "blood transfusion reaction" as the cause of death. I know that might well set the nurses on this forum to howling in protest, but it goes on.
Then there is the matter of diseases which may be transmitted by transfusion. The last time I saw an authoritative figure it was about 120 different diseases and climbing. Does anyone seriously think that the Red Cross, much less anybody else, tests for all those diseases, many of which are potentially fatal? Because the cost would be prohibitive they don't. but it gets even worse than that. Even though they do test for some of the most feared pathogens, it is not uncommon for the Red cross to go ahead and release the blood for use before the results are known. How does the phrase "crap shoot" sound?
There are also other ways one can be killed by transfusions. Thalesemics, sickle cell anemics, and others who require many transfusions of blood over a long time can be killed from volume overload, iron toxicity, and other problems related to the transfusions. Like I said, products with those kind of problems are not allowed on the market by the FDA, and yet blood is encouraged for the simple reason that a whole industry depends on the use of the product for its existence.
For those reasons, I have a brother, who is an RN and not a Dub, who insists that blood not be used on him except under the the most extenuating of circumstances and I don't blame him one bit. Don't get me wrong, I am not arguing the rightness or wrongness of the theological position here. All I am doing is laying out the answer to the question posed. Simply put, blood is a biological product which is dangerous to use and it should not be used as casually as it is today. But then, with an industry dedicated to promoting its use, it is no suprise it is.
There's your answer, at least you can make a more informed decision now.
Forscher