I don't really know where they even came up with this idea to begin with because humans obviously wouldn't be kosher even if blood drinking of kosher animals itself was ok (and from what I have learned it's not).
Muslims are the ones who commit human sacrifice.
It was a libel created by the Christian church...
http://en.wikipedia.org/wiki/Blood_libelEncyclopædia Britannica writes:
blood libel, also called blood accusation, the superstitious accusation that Jews ritually sacrifice the children of Christians at Passover to obtain blood for unleavened bread. It first emerged in medieval Europe in the 12th century and was revived sporadically in eastern and central Europe throughout the medieval and modern periods, often leading to the persecution of Jews.[11]
Professor Israel Jacob Yuval of the Hebrew University of Jerusalem published an article in 1993 that argues that blood libel may have originated in the 12th century from Christian views of Jewish behavior during the First Crusade. Some Jews committed suicide and killed their own children rather than be subjected to forced conversions. Yuval investigated Christian reports of these events and found that they were greatly distorted with claims that if Jews could kill their own children they could also kill the children of Christians. Yuval rejects the blood libel story as a fantasy of some Christians which could not contain any elements of truth because of the precarious nature of the Jewish minority's existence in Christian Europe.[12][13]
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Views of the Catholic Church[edit]
The attitude of the Roman Catholic Church towards these accusations and the cults venerating children supposedly killed by Jews has varied over time. The papacy generally opposed them, although it had problems in enforcing its opposition.
In 1911, the Dictionnaire apologétique de la foi catholique, an important French Catholic encyclopedia, published an analysis of the blood libel accusations.[62] This may be taken as being broadly representative of educated Catholic opinion in continental Europe at that time. The article noted that the popes had generally refrained from endorsing the blood libel, and it concluded that the accusations were unproven in a general sense, but it left open the possibility that some Jews had committed ritual murders of Christians. Other contemporary Catholic sources (notably the Jesuit periodical Civiltà cattolica) promoted the blood libel as truth.[63]
Today, the accusations are almost entirely discredited in Catholic circles, and the cults associated with them have fallen into disfavour. For example, Simon of Trent was deleted from the Calendar of Saints in 1965 and does not appear in the current (2000) edition of the Roman Martyrology.