They took the blood stand because the leaders needed another way to set JWs apart from other "christian" religions. Fred Franz just carried on Clayton J. Woodruff's crazy medical beliefs and came up with the blood thing. They've been locked to it ever since.
Many here will not know that in the early 1950s - during the worst of the polio epidemics - Drs. Salk and Sabin were working independently on a polio vaccine. Polio was so bad at the time that almost every school classroom had at least one student who had it, was crippled by it, or caught it during those years. One kid with polio could decimate an elementary school if not isolated immediately.
Around 1952-54 when Salk finally came out with his polio vaccine, the number of cases dropped immediately. Jehovah's Witnesses, however, most often refused to let their kids take the vaccine. Their avoidance of vaccines was leftover from the Golden Age and Consolation magazine days when Woodruff regularly published articles claiming that vaccines were poisonous - and actually caused diseases rather than preventing them.
I'm not sure if the Awake! ever published an article saying not to take the polio vaccine, but the word was out and none of the Witness families I knew would allow their kids to take the vaccine. I finally took the Sabin vaccine (on a sugar cube) at a free clinic in 1962, after I was old enough to make my own decisions. I don't know if my younger brother and sister ever took the vaccine.
Within ten years, polio became almost unknown in industrialized countries. My kids could not enter school unless they had been given the vaccine.
Another example of the Watchtower being on the wrong side of an issue. Jehovah's spirit needs to catch up on scientific facts before it directs the governing body and its writing committee.
JV